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 $217.71   12.512%   $244.9499   $244.95   $244.95   $244.90  
  Purchase #2 $114.53   7.204%   $122.7807   $122.78   $122.80   $122.80  
  Purchase #3 $130.45   9.599%   $142.9719   $142.97   $142.95   $143.00  
  Purchase #4 $213.56   8.460%   $231.6272   $231.63   $231.65   $231.60  
  Purchase #5 $85.72   4.526%   $89.5997   $89.60   $89.60   $89.60  
  Purchase #6 $213.70   13.622%   $242.8102   $242.81   $242.80   $242.80  
  Purchase #7 $180.57   12.427%   $203.0094   $203.01   $203.00   $203.00  
  7 purchase totals = $1,156.24       $1,277.7490   $1,277.75   $1,277.75   $1,277.70