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 $236.39   13.566%   $268.4587   $268.46   $268.45   $268.50  
  Purchase #2 $26.33   8.392%   $28.5396   $28.54   $28.55   $28.50  
  Purchase #3 $102.85   10.150%   $113.2893   $113.29   $113.30   $113.30  
  Purchase #4 $132.46   12.777%   $149.3844   $149.38   $149.40   $149.40  
  Purchase #5 $70.51   4.472%   $73.6632   $73.66   $73.65   $73.70  
  Purchase #6 $111.62   12.291%   $125.3392   $125.34   $125.35   $125.30  
  Purchase #7 $244.70   13.664%   $278.1358   $278.14   $278.15   $278.10  
  7 purchase totals = $924.86       $1,036.8102   $1,036.81   $1,036.85   $1,036.80