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 $179.41   4.604%   $187.67   $187.67   $187.65   $187.70  
  Purchase #2 $245.47   12.252%   $275.545   $275.55   $275.55   $275.50  
  Purchase #3 $73.84   11.641%   $82.4357   $82.44   $82.45   $82.40  
  Purchase #4 $59.72   10.534%   $66.0109   $66.01   $66.00   $66.00  
  Purchase #5 $51.76   12.153%   $58.0504   $58.05   $58.05   $58.10  
  Purchase #6 $47.86   5.537%   $50.51   $50.51   $50.50   $50.50  
  Purchase #7 $217.34   11.250%   $241.7908   $241.79   $241.80   $241.80  
  7 purchase totals = $875.40       $962.0128   $962.02   $962.00   $962.00