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 $244.89   9.163%   $267.3293   $267.33   $267.35   $267.30  
  Purchase #2 $199.72   13.399%   $226.4805   $226.48   $226.50   $226.50  
  Purchase #3 $238.87   3.404%   $247.0011   $247.00   $247.00   $247.00  
  Purchase #4 $68.56   11.804%   $76.6528   $76.65   $76.65   $76.70  
  Purchase #5 $20.84   7.653%   $22.4349   $22.43   $22.45   $22.40  
  Purchase #6 $246.82   5.844%   $261.2442   $261.24   $261.25   $261.20  
  Purchase #7 $54.47   9.179%   $59.4698   $59.47   $59.45   $59.50  
  7 purchase totals = $1,074.17       $1,160.6126   $1,160.60   $1,160.65   $1,160.60