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 $184.68   13.735%   $210.0458   $210.05   $210.05   $210.00  
  Purchase #2 $142.60   11.508%   $159.0104   $159.01   $159.00   $159.00  
  Purchase #3 $42.26   8.218%   $45.7329   $45.73   $45.75   $45.70  
  Purchase #4 $96.37   9.364%   $105.3941   $105.39   $105.40   $105.40  
  Purchase #5 $59.45   9.223%   $64.9331   $64.93   $64.95   $64.90  
  Purchase #6 $211.59   8.692%   $229.9814   $229.98   $230.00   $230.00  
  Purchase #7 $79.48   8.698%   $86.3932   $86.39   $86.40   $86.40  
  7 purchase totals = $816.43       $901.4909   $901.48   $901.55   $901.40