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 $215.78   6.512%   $229.8316   $229.83   $229.85   $229.80  
  Purchase #2 $24.83   8.699%   $26.99   $26.99   $27.00   $27.00  
  Purchase #3 $130.34   3.417%   $134.7937   $134.79   $134.80   $134.80  
  Purchase #4 $234.73   3.118%   $242.0489   $242.05   $242.05   $242.00  
  Purchase #5 $150.25   13.311%   $170.2498   $170.25   $170.25   $170.20  
  Purchase #6 $155.33   10.660%   $171.8882   $171.89   $171.90   $171.90  
  Purchase #7 $34.26   12.296%   $38.4726   $38.47   $38.45   $38.50  
  7 purchase totals = $945.52       $1,014.2748   $1,014.27   $1,014.30   $1,014.20