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 $60.98   8.308%   $66.0462   $66.05   $66.05   $66.00  
  Purchase #2 $149.53   9.421%   $163.6172   $163.62   $163.60   $163.60  
  Purchase #3 $109.55   13.168%   $123.9755   $123.98   $124.00   $124.00  
  Purchase #4 $64.52   11.438%   $71.8998   $71.90   $71.90   $71.90  
  Purchase #5 $164.81   6.527%   $175.5671   $175.57   $175.55   $175.60  
  Purchase #6 $161.66   9.643%   $177.2489   $177.25   $177.25   $177.20  
  Purchase #7 $44.46   8.767%   $48.3578   $48.36   $48.35   $48.40  
  7 purchase totals = $755.51       $826.7125   $826.73   $826.70   $826.70