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 $249.92   11.716%   $279.2006   $279.20   $279.20   $279.20  
  Purchase #2 $144.39   5.109%   $151.7669   $151.77   $151.75   $151.80  
  Purchase #3 $135.98   12.705%   $153.2563   $153.26   $153.25   $153.30  
  Purchase #4 $171.79   13.631%   $195.2067   $195.21   $195.20   $195.20  
  Purchase #5 $158.70   9.785%   $174.2288   $174.23   $174.25   $174.20  
  Purchase #6 $98.43   7.428%   $105.7414   $105.74   $105.75   $105.70  
  Purchase #7 $119.83   12.645%   $134.9825   $134.98   $135.00   $135.00  
  7 purchase totals = $1,079.04       $1,194.3832   $1,194.39   $1,194.40   $1,194.40