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 $208.61   13.758%   $237.3106   $237.31   $237.30   $237.30  
  Purchase #2 $162.35   12.588%   $182.7866   $182.79   $182.80   $182.80  
  Purchase #3 $75.96   9.777%   $83.3866   $83.39   $83.40   $83.40  
  Purchase #4 $98.88   7.578%   $106.3731   $106.37   $106.35   $106.40  
  Purchase #5 $59.27   9.659%   $64.9949   $64.99   $65.00   $65.00  
  Purchase #6 $9.28   13.210%   $10.5059   $10.51   $10.50   $10.50  
  Purchase #7 $98.82   3.872%   $102.6463   $102.65   $102.65   $102.60  
  7 purchase totals = $713.17       $788.0040   $788.01   $788.00   $788.00