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 $93.65   10.244%   $103.2435   $103.24   $103.25   $103.20  
  Purchase #2 $64.88   9.594%   $71.1046   $71.10   $71.10   $71.10  
  Purchase #3 $62.39   5.382%   $65.7478   $65.75   $65.75   $65.70  
  Purchase #4 $86.64   13.275%   $98.1415   $98.14   $98.15   $98.10  
  Purchase #5 $171.43   12.360%   $192.6187   $192.62   $192.60   $192.60  
  Purchase #6 $119.45   5.687%   $126.2431   $126.24   $126.25   $126.20  
  Purchase #7 $124.38   9.180%   $135.7981   $135.80   $135.80   $135.80  
  7 purchase totals = $722.82       $792.8973   $792.89   $792.90   $792.70