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 $56.50   12.368%   $63.4879   $63.49   $63.50   $63.50  
  Purchase #2 $26.46   8.128%   $28.6107   $28.61   $28.60   $28.60  
  Purchase #3 $125.37   3.111%   $129.2703   $129.27   $129.25   $129.30  
  Purchase #4 $92.32   4.826%   $96.7754   $96.78   $96.80   $96.80  
  Purchase #5 $152.90   13.451%   $173.4666   $173.47   $173.45   $173.50  
  Purchase #6 $73.94   3.578%   $76.5856   $76.59   $76.60   $76.60  
  Purchase #7 $135.72   12.817%   $153.1152   $153.12   $153.10   $153.10  
  7 purchase totals = $663.21       $721.3117   $721.33   $721.30   $721.40