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 $187.59   8.562%   $203.6515   $203.65   $203.65   $203.70  
  Purchase #2 $92.73   12.534%   $104.3528   $104.35   $104.35   $104.40  
  Purchase #3 $36.53   11.239%   $40.6356   $40.64   $40.65   $40.60  
  Purchase #4 $132.48   13.305%   $150.1065   $150.11   $150.10   $150.10  
  Purchase #5 $168.72   4.407%   $176.1555   $176.16   $176.15   $176.20  
  Purchase #6 $125.70   8.393%   $136.25   $136.25   $136.25   $136.30  
  Purchase #7 $48.36   12.595%   $54.4509   $54.45   $54.45   $54.50  
  7 purchase totals = $792.11       $865.6028   $865.61   $865.60   $865.80