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 $54.75   13.438%   $62.1073   $62.11   $62.10   $62.10  
  Purchase #2 $229.99   7.475%   $247.1818   $247.18   $247.20   $247.20  
  Purchase #3 $92.49   5.364%   $97.4512   $97.45   $97.45   $97.50  
  Purchase #4 $72.86   9.289%   $79.628   $79.63   $79.65   $79.60  
  Purchase #5 $57.60   4.790%   $60.359   $60.36   $60.35   $60.40  
  Purchase #6 $176.45   4.446%   $184.295   $184.30   $184.30   $184.30  
  Purchase #7 $127.68   10.657%   $141.2869   $141.29   $141.30   $141.30  
  7 purchase totals = $811.82       $872.3092   $872.32   $872.35   $872.40