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 $83.71   13.669%   $95.1523   $95.15   $95.15   $95.20  
  Purchase #2 $32.84   11.843%   $36.7292   $36.73   $36.75   $36.70  
  Purchase #3 $120.70   12.184%   $135.4061   $135.41   $135.40   $135.40  
  Purchase #4 $130.52   8.476%   $141.5829   $141.58   $141.60   $141.60  
  Purchase #5 $205.52   10.586%   $227.2763   $227.28   $227.30   $227.30  
  Purchase #6 $52.32   9.336%   $57.2046   $57.20   $57.20   $57.20  
  Purchase #7 $58.69   9.324%   $64.1623   $64.16   $64.15   $64.20  
  7 purchase totals = $684.30       $757.5137   $757.51   $757.55   $757.60