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 $210.51   8.276%   $227.9318   $227.93   $227.95   $227.90  
  Purchase #2 $202.88   13.339%   $229.9422   $229.94   $229.95   $229.90  
  Purchase #3 $25.26   5.599%   $26.6743   $26.67   $26.65   $26.70  
  Purchase #4 $96.85   6.673%   $103.3128   $103.31   $103.30   $103.30  
  Purchase #5 $28.73   4.758%   $30.097   $30.10   $30.10   $30.10  
  Purchase #6 $249.56   4.433%   $260.623   $260.62   $260.60   $260.60  
  Purchase #7 $148.63   13.764%   $169.0874   $169.09   $169.10   $169.10  
  7 purchase totals = $962.42       $1,047.6685   $1,047.66   $1,047.65   $1,047.60