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 $58.68   10.594%   $64.8966   $64.90   $64.90   $64.90  
  Purchase #2 $113.57   7.263%   $121.8186   $121.82   $121.80   $121.80  
  Purchase #3 $246.34   6.197%   $261.6057   $261.61   $261.60   $261.60  
  Purchase #4 $51.32   13.132%   $58.0593   $58.06   $58.05   $58.10  
  Purchase #5 $173.59   5.828%   $183.7068   $183.71   $183.70   $183.70  
  Purchase #6 $46.59   6.237%   $49.4958   $49.50   $49.50   $49.50  
  Purchase #7 $56.87   5.707%   $60.1156   $60.12   $60.10   $60.10  
  7 purchase totals = $746.96       $799.6984   $799.72   $799.65   $799.70