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 $104.59   5.728%   $110.5809   $110.58   $110.60   $110.60  
  Purchase #2 $233.87   6.329%   $248.6716   $248.67   $248.65   $248.70  
  Purchase #3 $14.30   13.131%   $16.1777   $16.18   $16.20   $16.20  
  Purchase #4 $229.88   4.546%   $240.3303   $240.33   $240.35   $240.30  
  Purchase #5 $235.55   4.729%   $246.6892   $246.69   $246.70   $246.70  
  Purchase #6 $176.83   4.812%   $185.3391   $185.34   $185.35   $185.30  
  Purchase #7 $206.50   9.455%   $226.0246   $226.02   $226.00   $226.00  
  7 purchase totals = $1,201.52       $1,273.8134   $1,273.81   $1,273.85   $1,273.80