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 $193.41   7.646%   $208.1981   $208.20   $208.20   $208.20  
  Purchase #2 $117.50   4.276%   $122.5243   $122.52   $122.50   $122.50  
  Purchase #3 $46.32   9.232%   $50.5963   $50.60   $50.60   $50.60  
  Purchase #4 $158.77   13.769%   $180.631   $180.63   $180.65   $180.60  
  Purchase #5 $113.26   10.390%   $125.0277   $125.03   $125.05   $125.00  
  Purchase #6 $187.87   12.498%   $211.35   $211.35   $211.35   $211.40  
  Purchase #7 $131.51   4.291%   $137.1531   $137.15   $137.15   $137.20  
  7 purchase totals = $948.64       $1,035.4805   $1,035.48   $1,035.50   $1,035.50