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 $219.43   13.650%   $249.3822   $249.38   $249.40   $249.40  
  Purchase #2 $40.68   7.114%   $43.574   $43.57   $43.55   $43.60  
  Purchase #3 $155.93   7.832%   $168.1424   $168.14   $168.15   $168.10  
  Purchase #4 $118.95   6.227%   $126.357   $126.36   $126.35   $126.40  
  Purchase #5 $206.30   11.569%   $230.1668   $230.17   $230.15   $230.20  
  Purchase #6 $126.40   10.695%   $139.9185   $139.92   $139.90   $139.90  
  Purchase #7 $185.37   6.671%   $197.736   $197.74   $197.75   $197.70  
  7 purchase totals = $1,053.06       $1,155.2769   $1,155.28   $1,155.25   $1,155.30