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 $61.67   6.258%   $65.5293   $65.53   $65.55   $65.50  
  Purchase #2 $76.63   13.869%   $87.2578   $87.26   $87.25   $87.30  
  Purchase #3 $182.62   13.584%   $207.4271   $207.43   $207.45   $207.40  
  Purchase #4 $104.42   6.558%   $111.2679   $111.27   $111.25   $111.30  
  Purchase #5 $203.29   7.772%   $219.0897   $219.09   $219.10   $219.10  
  Purchase #6 $19.35   5.650%   $20.4433   $20.44   $20.45   $20.40  
  Purchase #7 $126.44   13.487%   $143.493   $143.49   $143.50   $143.50  
  7 purchase totals = $774.42       $854.5081   $854.51   $854.55   $854.50