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 $194.71   4.653%   $203.7699   $203.77   $203.75   $203.80  
  Purchase #2 $74.47   10.353%   $82.1799   $82.18   $82.20   $82.20  
  Purchase #3 $151.34   11.267%   $168.3915   $168.39   $168.40   $168.40  
  Purchase #4 $126.77   8.156%   $137.1094   $137.11   $137.10   $137.10  
  Purchase #5 $161.80   9.792%   $177.6435   $177.64   $177.65   $177.60  
  Purchase #6 $64.86   6.579%   $69.1271   $69.13   $69.15   $69.10  
  Purchase #7 $120.39   4.404%   $125.692   $125.69   $125.70   $125.70  
  7 purchase totals = $894.34       $963.9133   $963.91   $963.95   $963.90