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 $56.31   13.346%   $63.8251   $63.83   $63.85   $63.80  
  Purchase #2 $193.67   10.480%   $213.9666   $213.97   $213.95   $214.00  
  Purchase #3 $53.78   11.502%   $59.9658   $59.97   $59.95   $60.00  
  Purchase #4 $127.89   9.363%   $139.8643   $139.86   $139.85   $139.90  
  Purchase #5 $241.33   7.299%   $258.9447   $258.94   $258.95   $258.90  
  Purchase #6 $47.45   8.535%   $51.4999   $51.50   $51.50   $51.50  
  Purchase #7 $22.26   9.589%   $24.3945   $24.39   $24.40   $24.40  
  7 purchase totals = $742.69       $812.4609   $812.46   $812.45   $812.50