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 $225.64   9.347%   $246.7306   $246.73   $246.75   $246.70  
  Purchase #2 $242.63   8.671%   $263.6684   $263.67   $263.65   $263.70  
  Purchase #3 $32.70   4.647%   $34.2196   $34.22   $34.20   $34.20  
  Purchase #4 $13.81   5.474%   $14.566   $14.57   $14.55   $14.60  
  Purchase #5 $85.67   8.496%   $92.9485   $92.95   $92.95   $92.90  
  Purchase #6 $147.57   13.198%   $167.0463   $167.05   $167.05   $167.00  
  Purchase #7 $123.26   7.776%   $132.8447   $132.84   $132.85   $132.80  
  7 purchase totals = $871.28       $952.0241   $952.03   $952.00   $951.90