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 $48.83   5.491%   $51.5113   $51.51   $51.50   $51.50  
  Purchase #2 $176.64   4.849%   $185.2053   $185.21   $185.20   $185.20  
  Purchase #3 $58.81   12.254%   $66.0166   $66.02   $66.00   $66.00  
  Purchase #4 $17.97   12.731%   $20.2578   $20.26   $20.25   $20.30  
  Purchase #5 $47.34   5.774%   $50.0734   $50.07   $50.05   $50.10  
  Purchase #6 $101.51   6.592%   $108.2015   $108.20   $108.20   $108.20  
  Purchase #7 $16.54   6.495%   $17.6143   $17.61   $17.60   $17.60  
  7 purchase totals = $467.64       $498.8802   $498.88   $498.80   $498.90