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 $146.62   11.304%   $163.1939   $163.19   $163.20   $163.20  
  Purchase #2 $201.60   6.868%   $215.4459   $215.45   $215.45   $215.40  
  Purchase #3 $169.40   4.638%   $177.2568   $177.26   $177.25   $177.30  
  Purchase #4 $95.89   8.470%   $104.0119   $104.01   $104.00   $104.00  
  Purchase #5 $51.56   3.695%   $53.4651   $53.47   $53.45   $53.50  
  Purchase #6 $171.90   9.460%   $188.1617   $188.16   $188.15   $188.20  
  Purchase #7 $48.74   7.598%   $52.4433   $52.44   $52.45   $52.40  
  7 purchase totals = $885.71       $953.9786   $953.98   $953.95   $954.00