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 $119.62   5.672%   $126.4048   $126.40   $126.40   $126.40  
  Purchase #2 $215.68   6.842%   $230.4368   $230.44   $230.45   $230.40  
  Purchase #3 $171.49   9.620%   $187.9873   $187.99   $188.00   $188.00  
  Purchase #4 $248.80   7.678%   $267.9029   $267.90   $267.90   $267.90  
  Purchase #5 $249.84   12.233%   $280.4029   $280.40   $280.40   $280.40  
  Purchase #6 $146.25   10.838%   $162.1006   $162.10   $162.10   $162.10  
  Purchase #7 $61.33   11.197%   $68.1971   $68.20   $68.20   $68.20  
  7 purchase totals = $1,213.01       $1,323.4324   $1,323.43   $1,323.45   $1,323.40