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 $119.56   11.686%   $133.5318   $133.53   $133.55   $133.50  
  Purchase #2 $250.31   8.571%   $271.7641   $271.76   $271.75   $271.80  
  Purchase #3 $82.91   7.487%   $89.1175   $89.12   $89.10   $89.10  
  Purchase #4 $122.93   5.489%   $129.6776   $129.68   $129.70   $129.70  
  Purchase #5 $95.50   3.380%   $98.7279   $98.73   $98.75   $98.70  
  Purchase #6 $151.80   10.435%   $167.6403   $167.64   $167.65   $167.60  
  Purchase #7 $99.80   5.321%   $105.1104   $105.11   $105.10   $105.10  
  7 purchase totals = $922.81       $995.5696   $995.57   $995.60   $995.50