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 $135.57   13.291%   $153.5886   $153.59   $153.60   $153.60  
  Purchase #2 $229.86   12.553%   $258.7143   $258.71   $258.70   $258.70  
  Purchase #3 $153.63   3.393%   $158.8427   $158.84   $158.85   $158.80  
  Purchase #4 $132.26   4.399%   $138.0781   $138.08   $138.10   $138.10  
  Purchase #5 $83.98   10.623%   $92.9012   $92.90   $92.90   $92.90  
  Purchase #6 $191.31   12.312%   $214.8641   $214.86   $214.85   $214.90  
  Purchase #7 $42.45   10.335%   $46.8372   $46.84   $46.85   $46.80  
  7 purchase totals = $969.06       $1,063.8262   $1,063.82   $1,063.85   $1,063.80