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 $52.57   8.755%   $57.1725   $57.17   $57.15   $57.20  
  Purchase #2 $46.94   13.138%   $53.107   $53.11   $53.10   $53.10  
  Purchase #3 $22.61   8.823%   $24.6049   $24.60   $24.60   $24.60  
  Purchase #4 $210.28   9.217%   $229.6615   $229.66   $229.65   $229.70  
  Purchase #5 $96.89   5.624%   $102.3391   $102.34   $102.35   $102.30  
  Purchase #6 $44.50   8.158%   $48.1303   $48.13   $48.15   $48.10  
  Purchase #7 $248.47   4.136%   $258.7467   $258.75   $258.75   $258.70  
  7 purchase totals = $722.26       $773.7620   $773.76   $773.75   $773.70