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 $227.83   11.171%   $253.2809   $253.28   $253.30   $253.30  
  Purchase #2 $171.95   4.622%   $179.8975   $179.90   $179.90   $179.90  
  Purchase #3 $143.96   4.725%   $150.7621   $150.76   $150.75   $150.80  
  Purchase #4 $151.67   11.614%   $169.285   $169.29   $169.30   $169.30  
  Purchase #5 $81.97   3.433%   $84.784   $84.78   $84.80   $84.80  
  Purchase #6 $200.87   8.350%   $217.6426   $217.64   $217.65   $217.60  
  Purchase #7 $54.67   13.443%   $62.0193   $62.02   $62.00   $62.00  
  7 purchase totals = $1,032.92       $1,117.6714   $1,117.67   $1,117.70   $1,117.70