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 $6.58   3.635%   $6.8192   $6.82   $6.80   $6.80  
  Purchase #2 $152.47   5.791%   $161.2995   $161.30   $161.30   $161.30  
  Purchase #3 $73.98   4.717%   $77.4696   $77.47   $77.45   $77.50  
  Purchase #4 $189.55   7.773%   $204.2837   $204.28   $204.30   $204.30  
  Purchase #5 $122.40   7.505%   $131.5861   $131.59   $131.60   $131.60  
  Purchase #6 $35.54   12.798%   $40.0884   $40.09   $40.10   $40.10  
  Purchase #7 $55.71   13.333%   $63.1378   $63.14   $63.15   $63.10  
  7 purchase totals = $636.23       $684.6843   $684.69   $684.70   $684.70