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 $119.87   10.608%   $132.5858   $132.59   $132.60   $132.60  
  Purchase #2 $30.56   7.271%   $32.782   $32.78   $32.80   $32.80  
  Purchase #3 $22.41   11.613%   $25.0125   $25.01   $25.00   $25.00  
  Purchase #4 $104.97   11.868%   $117.4278   $117.43   $117.45   $117.40  
  Purchase #5 $146.45   9.226%   $159.9615   $159.96   $159.95   $160.00  
  Purchase #6 $217.45   4.490%   $227.2135   $227.21   $227.20   $227.20  
  Purchase #7 $6.86   5.440%   $7.2332   $7.23   $7.25   $7.20  
  7 purchase totals = $648.57       $702.2163   $702.21   $702.25   $702.20