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 $190.63   10.695%   $211.0179   $211.02   $211.00   $211.00  
  Purchase #2 $245.95   11.653%   $274.6106   $274.61   $274.60   $274.60  
  Purchase #3 $130.35   12.229%   $146.2905   $146.29   $146.30   $146.30  
  Purchase #4 $164.94   5.135%   $173.4097   $173.41   $173.40   $173.40  
  Purchase #5 $72.48   5.859%   $76.7266   $76.73   $76.75   $76.70  
  Purchase #6 $14.46   3.151%   $14.9156   $14.92   $14.90   $14.90  
  Purchase #7 $170.65   5.738%   $180.4419   $180.44   $180.45   $180.40  
  7 purchase totals = $989.46       $1,077.4128   $1,077.42   $1,077.40   $1,077.30