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 $48.27   9.149%   $52.6862   $52.69   $52.70   $52.70  
  Purchase #2 $96.90   11.163%   $107.7169   $107.72   $107.70   $107.70  
  Purchase #3 $115.34   7.275%   $123.731   $123.73   $123.75   $123.70  
  Purchase #4 $229.48   10.614%   $253.837   $253.84   $253.85   $253.80  
  Purchase #5 $236.86   9.759%   $259.9752   $259.98   $260.00   $260.00  
  Purchase #6 $126.41   6.606%   $134.7606   $134.76   $134.75   $134.80  
  Purchase #7 $78.88   8.136%   $85.2977   $85.30   $85.30   $85.30  
  7 purchase totals = $932.14       $1,018.0046   $1,018.02   $1,018.05   $1,018.00