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 $58.53   8.318%   $63.3985   $63.40   $63.40   $63.40  
  Purchase #2 $126.45   4.296%   $131.8823   $131.88   $131.90   $131.90  
  Purchase #3 $6.78   11.379%   $7.5515   $7.55   $7.55   $7.60  
  Purchase #4 $179.73   6.574%   $191.5455   $191.55   $191.55   $191.50  
  Purchase #5 $92.46   3.831%   $96.0021   $96.00   $96.00   $96.00  
  Purchase #6 $209.56   11.670%   $234.0157   $234.02   $234.00   $234.00  
  Purchase #7 $33.42   5.342%   $35.2053   $35.21   $35.20   $35.20  
  7 purchase totals = $706.93       $759.6009   $759.61   $759.60   $759.60