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 $58.37   6.532%   $62.1827   $62.18   $62.20   $62.20  
  Purchase #2 $48.44   11.139%   $53.8357   $53.84   $53.85   $53.80  
  Purchase #3 $196.84   6.485%   $209.6051   $209.61   $209.60   $209.60  
  Purchase #4 $28.77   10.738%   $31.8593   $31.86   $31.85   $31.90  
  Purchase #5 $82.87   13.797%   $94.3036   $94.30   $94.30   $94.30  
  Purchase #6 $217.31   7.211%   $232.9802   $232.98   $233.00   $233.00  
  Purchase #7 $232.75   10.317%   $256.7628   $256.76   $256.75   $256.80  
  7 purchase totals = $865.35       $941.5294   $941.53   $941.55   $941.60