Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.97   10.402%   $267.1397   $267.14   $267.15   $267.10  
  Purchase #2 $198.41   10.706%   $219.6518   $219.65   $219.65   $219.70  
  Purchase #3 $163.50   13.750%   $185.9813   $185.98   $186.00   $186.00  
  Purchase #4 $240.81   4.812%   $252.3978   $252.40   $252.40   $252.40  
  Purchase #5 $155.30   4.247%   $161.8956   $161.90   $161.90   $161.90  
  Purchase #6 $221.73   6.339%   $235.7855   $235.79   $235.80   $235.80  
  Purchase #7 $106.27   13.721%   $120.8513   $120.85   $120.85   $120.90  
  7 purchase totals = $1,327.99       $1,443.7030   $1,443.71   $1,443.75   $1,443.80