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 $60.29   4.756%   $63.1574   $63.16   $63.15   $63.20  
  Purchase #2 $246.37   3.399%   $254.7441   $254.74   $254.75   $254.70  
  Purchase #3 $70.30   6.140%   $74.6164   $74.62   $74.60   $74.60  
  Purchase #4 $189.95   8.649%   $206.3788   $206.38   $206.40   $206.40  
  Purchase #5 $14.61   7.348%   $15.6835   $15.68   $15.70   $15.70  
  Purchase #6 $180.79   7.474%   $194.3022   $194.30   $194.30   $194.30  
  Purchase #7 $139.33   5.816%   $147.4334   $147.43   $147.45   $147.40  
  7 purchase totals = $901.64       $956.3158   $956.31   $956.35   $956.30