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 $204.83   5.726%   $216.5586   $216.56   $216.55   $216.60  
  Purchase #2 $105.52   10.148%   $116.2282   $116.23   $116.25   $116.20  
  Purchase #3 $149.95   11.354%   $166.9753   $166.98   $167.00   $167.00  
  Purchase #4 $58.85   12.709%   $66.3292   $66.33   $66.35   $66.30  
  Purchase #5 $51.71   12.605%   $58.228   $58.23   $58.25   $58.20  
  Purchase #6 $63.96   7.499%   $68.7564   $68.76   $68.75   $68.80  
  Purchase #7 $246.49   6.247%   $261.8882   $261.89   $261.90   $261.90  
  7 purchase totals = $881.31       $954.9639   $954.98   $955.05   $955.00