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 $197.71   13.390%   $224.1834   $224.18   $224.20   $224.20  
  Purchase #2 $43.49   6.571%   $46.3477   $46.35   $46.35   $46.30  
  Purchase #3 $157.48   12.391%   $176.9933   $176.99   $177.00   $177.00  
  Purchase #4 $119.48   4.794%   $125.2079   $125.21   $125.20   $125.20  
  Purchase #5 $53.61   9.443%   $58.6724   $58.67   $58.65   $58.70  
  Purchase #6 $239.47   7.403%   $257.198   $257.20   $257.20   $257.20  
  Purchase #7 $208.70   13.120%   $236.0814   $236.08   $236.10   $236.10  
  7 purchase totals = $1,019.94       $1,124.6841   $1,124.68   $1,124.70   $1,124.70