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 $193.85   11.385%   $215.9198   $215.92   $215.90   $215.90  
  Purchase #2 $230.37   11.269%   $256.3304   $256.33   $256.35   $256.30  
  Purchase #3 $20.87   4.290%   $21.7653   $21.77   $21.75   $21.80  
  Purchase #4 $120.34   3.407%   $124.44   $124.44   $124.45   $124.40  
  Purchase #5 $68.53   11.198%   $76.204   $76.20   $76.20   $76.20  
  Purchase #6 $61.72   5.463%   $65.0918   $65.09   $65.10   $65.10  
  Purchase #7 $169.57   11.200%   $188.5618   $188.56   $188.55   $188.60  
  7 purchase totals = $865.25       $948.3131   $948.31   $948.30   $948.30