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 $246.25   11.683%   $275.0194   $275.02   $275.00   $275.00  
  Purchase #2 $88.95   11.439%   $99.125   $99.13   $99.15   $99.10  
  Purchase #3 $62.25   3.639%   $64.5153   $64.52   $64.50   $64.50  
  Purchase #4 $66.30   10.290%   $73.1223   $73.12   $73.10   $73.10  
  Purchase #5 $248.44   7.375%   $266.7625   $266.76   $266.75   $266.80  
  Purchase #6 $84.86   9.525%   $92.9429   $92.94   $92.95   $92.90  
  Purchase #7 $168.84   11.418%   $188.1182   $188.12   $188.10   $188.10  
  7 purchase totals = $965.89       $1,059.6056   $1,059.61   $1,059.55   $1,059.50