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 $208.99   13.461%   $237.1221   $237.12   $237.10   $237.10  
  Purchase #2 $180.56   9.440%   $197.6049   $197.60   $197.60   $197.60  
  Purchase #3 $28.74   10.576%   $31.7795   $31.78   $31.80   $31.80  
  Purchase #4 $116.30   5.559%   $122.7651   $122.77   $122.75   $122.80  
  Purchase #5 $132.82   8.272%   $143.8069   $143.81   $143.80   $143.80  
  Purchase #6 $161.59   3.673%   $167.5252   $167.53   $167.55   $167.50  
  Purchase #7 $62.57   5.726%   $66.1528   $66.15   $66.15   $66.20  
  7 purchase totals = $891.57       $966.7565   $966.76   $966.75   $966.80