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 $185.85   10.253%   $204.9052   $204.91   $204.90   $204.90  
  Purchase #2 $58.77   7.855%   $63.3864   $63.39   $63.40   $63.40  
  Purchase #3 $127.76   6.105%   $135.5597   $135.56   $135.55   $135.60  
  Purchase #4 $161.75   3.345%   $167.1605   $167.16   $167.15   $167.20  
  Purchase #5 $132.81   8.714%   $144.3831   $144.38   $144.40   $144.40  
  Purchase #6 $216.54   6.743%   $231.1413   $231.14   $231.15   $231.10  
  Purchase #7 $48.77   12.369%   $54.8024   $54.80   $54.80   $54.80  
  7 purchase totals = $932.25       $1,001.3386   $1,001.34   $1,001.35   $1,001.40