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 $91.74   11.481%   $102.2727   $102.27   $102.25   $102.30  
  Purchase #2 $79.33   7.162%   $85.0116   $85.01   $85.00   $85.00  
  Purchase #3 $84.82   13.683%   $96.4259   $96.43   $96.45   $96.40  
  Purchase #4 $131.62   3.691%   $136.4781   $136.48   $136.50   $136.50  
  Purchase #5 $118.86   5.534%   $125.4377   $125.44   $125.45   $125.40  
  Purchase #6 $142.46   5.259%   $149.952   $149.95   $149.95   $150.00  
  Purchase #7 $26.39   13.109%   $29.8495   $29.85   $29.85   $29.80  
  7 purchase totals = $675.22       $725.4275   $725.43   $725.45   $725.40