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 $241.37   6.785%   $257.747   $257.75   $257.75   $257.70  
  Purchase #2 $37.33   11.871%   $41.7614   $41.76   $41.75   $41.80  
  Purchase #3 $27.36   4.185%   $28.505   $28.51   $28.50   $28.50  
  Purchase #4 $6.96   7.342%   $7.471   $7.47   $7.45   $7.50  
  Purchase #5 $124.73   4.190%   $129.9562   $129.96   $129.95   $130.00  
  Purchase #6 $165.61   13.297%   $187.6312   $187.63   $187.65   $187.60  
  Purchase #7 $50.64   9.847%   $55.6265   $55.63   $55.65   $55.60  
  7 purchase totals = $654.00       $708.6983   $708.71   $708.70   $708.70