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 $44.82   9.583%   $49.1151   $49.12   $49.10   $49.10  
  Purchase #2 $75.43   12.329%   $84.7298   $84.73   $84.75   $84.70  
  Purchase #3 $36.75   7.518%   $39.5129   $39.51   $39.50   $39.50  
  Purchase #4 $220.56   9.454%   $241.4117   $241.41   $241.40   $241.40  
  Purchase #5 $42.29   8.375%   $45.8318   $45.83   $45.85   $45.80  
  Purchase #6 $62.49   11.421%   $69.627   $69.63   $69.65   $69.60  
  Purchase #7 $113.79   7.296%   $122.0921   $122.09   $122.10   $122.10  
  7 purchase totals = $596.13       $652.3204   $652.32   $652.35   $652.20