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 $146.43   3.842%   $152.0558   $152.06   $152.05   $152.10  
  Purchase #2 $93.26   4.230%   $97.2049   $97.20   $97.20   $97.20  
  Purchase #3 $154.52   13.208%   $174.929   $174.93   $174.95   $174.90  
  Purchase #4 $65.42   5.225%   $68.8382   $68.84   $68.85   $68.80  
  Purchase #5 $69.82   12.293%   $78.403   $78.40   $78.40   $78.40  
  Purchase #6 $94.69   6.327%   $100.681   $100.68   $100.70   $100.70  
  Purchase #7 $45.60   11.579%   $50.88   $50.88   $50.90   $50.90  
  7 purchase totals = $669.74       $722.9919   $722.99   $723.05   $723.00