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 $61.35   9.808%   $67.3672   $67.37   $67.35   $67.40  
  Purchase #2 $205.29   9.164%   $224.1028   $224.10   $224.10   $224.10  
  Purchase #3 $26.74   7.616%   $28.7765   $28.78   $28.80   $28.80  
  Purchase #4 $42.74   13.665%   $48.5804   $48.58   $48.60   $48.60  
  Purchase #5 $239.45   12.672%   $269.7931   $269.79   $269.80   $269.80  
  Purchase #6 $26.46   10.636%   $29.2743   $29.27   $29.25   $29.30  
  Purchase #7 $224.82   11.391%   $250.4292   $250.43   $250.45   $250.40  
  7 purchase totals = $826.85       $918.3235   $918.32   $918.35   $918.40