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 $211.89   10.593%   $234.3355   $234.34   $234.35   $234.30  
  Purchase #2 $9.74   5.261%   $10.2524   $10.25   $10.25   $10.30  
  Purchase #3 $62.36   12.198%   $69.9667   $69.97   $69.95   $70.00  
  Purchase #4 $8.94   10.336%   $9.864   $9.86   $9.85   $9.90  
  Purchase #5 $248.75   4.715%   $260.4786   $260.48   $260.50   $260.50  
  Purchase #6 $50.73   3.112%   $52.3087   $52.31   $52.30   $52.30  
  Purchase #7 $95.79   6.722%   $102.229   $102.23   $102.25   $102.20  
  7 purchase totals = $688.20       $739.4349   $739.44   $739.45   $739.50