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 $239.35   11.794%   $267.5789   $267.58   $267.60   $267.60  
  Purchase #2 $81.45   13.341%   $92.3162   $92.32   $92.30   $92.30  
  Purchase #3 $221.37   11.871%   $247.6488   $247.65   $247.65   $247.60  
  Purchase #4 $58.96   13.705%   $67.0405   $67.04   $67.05   $67.00  
  Purchase #5 $178.77   9.227%   $195.2651   $195.27   $195.25   $195.30  
  Purchase #6 $127.50   11.300%   $141.9075   $141.91   $141.90   $141.90  
  Purchase #7 $26.63   10.695%   $29.4781   $29.48   $29.50   $29.50  
  7 purchase totals = $934.03       $1,041.2351   $1,041.25   $1,041.25   $1,041.20