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 $54.66   4.542%   $57.1427   $57.14   $57.15   $57.10  
  Purchase #2 $106.98   11.753%   $119.5534   $119.55   $119.55   $119.60  
  Purchase #3 $193.78   7.698%   $208.6972   $208.70   $208.70   $208.70  
  Purchase #4 $59.89   8.350%   $64.8908   $64.89   $64.90   $64.90  
  Purchase #5 $136.52   3.218%   $140.9132   $140.91   $140.90   $140.90  
  Purchase #6 $164.31   8.106%   $177.629   $177.63   $177.65   $177.60  
  Purchase #7 $191.58   10.517%   $211.7285   $211.73   $211.75   $211.70  
  7 purchase totals = $907.72       $980.5548   $980.55   $980.60   $980.50