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 $236.42   11.473%   $263.5445   $263.54   $263.55   $263.50  
  Purchase #2 $155.97   9.363%   $170.5735   $170.57   $170.55   $170.60  
  Purchase #3 $73.98   7.285%   $79.3694   $79.37   $79.35   $79.40  
  Purchase #4 $178.29   9.582%   $195.3737   $195.37   $195.35   $195.40  
  Purchase #5 $177.35   9.380%   $193.9854   $193.99   $194.00   $194.00  
  Purchase #6 $75.91   8.103%   $82.061   $82.06   $82.05   $82.10  
  Purchase #7 $53.40   9.689%   $58.5739   $58.57   $58.55   $58.60  
  7 purchase totals = $951.32       $1,043.4814   $1,043.47   $1,043.40   $1,043.60