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 $61.43   8.490%   $66.6454   $66.65   $66.65   $66.60  
  Purchase #2 $200.98   11.314%   $223.7189   $223.72   $223.70   $223.70  
  Purchase #3 $161.38   12.836%   $182.0947   $182.09   $182.10   $182.10  
  Purchase #4 $235.87   5.120%   $247.9465   $247.95   $247.95   $247.90  
  Purchase #5 $32.69   8.496%   $35.4673   $35.47   $35.45   $35.50  
  Purchase #6 $145.56   8.673%   $158.1844   $158.18   $158.20   $158.20  
  Purchase #7 $55.84   11.128%   $62.0539   $62.05   $62.05   $62.10  
  7 purchase totals = $893.75       $976.1111   $976.11   $976.10   $976.10