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 $249.62   5.386%   $263.0645   $263.06   $263.05   $263.10  
  Purchase #2 $100.32   4.504%   $104.8384   $104.84   $104.85   $104.80  
  Purchase #3 $53.37   13.524%   $60.5878   $60.59   $60.60   $60.60  
  Purchase #4 $197.63   8.794%   $215.0096   $215.01   $215.00   $215.00  
  Purchase #5 $137.32   8.872%   $149.503   $149.50   $149.50   $149.50  
  Purchase #6 $70.33   11.756%   $78.598   $78.60   $78.60   $78.60  
  Purchase #7 $39.38   4.244%   $41.0513   $41.05   $41.05   $41.10  
  7 purchase totals = $847.97       $912.6526   $912.65   $912.65   $912.70