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 $58.62   6.602%   $62.4901   $62.49   $62.50   $62.50  
  Purchase #2 $214.49   7.324%   $230.1992   $230.20   $230.20   $230.20  
  Purchase #3 $89.71   8.446%   $97.2869   $97.29   $97.30   $97.30  
  Purchase #4 $236.83   6.229%   $251.5821   $251.58   $251.60   $251.60  
  Purchase #5 $43.51   5.315%   $45.8226   $45.82   $45.80   $45.80  
  Purchase #6 $81.35   9.641%   $89.193   $89.19   $89.20   $89.20  
  Purchase #7 $187.77   9.720%   $206.0212   $206.02   $206.00   $206.00  
  7 purchase totals = $912.28       $982.5951   $982.59   $982.60   $982.60