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 $237.43   9.593%   $260.2067   $260.21   $260.20   $260.20  
  Purchase #2 $96.76   5.783%   $102.3556   $102.36   $102.35   $102.40  
  Purchase #3 $86.92   6.458%   $92.5333   $92.53   $92.55   $92.50  
  Purchase #4 $172.90   8.873%   $188.2414   $188.24   $188.25   $188.20  
  Purchase #5 $204.37   6.205%   $217.0512   $217.05   $217.05   $217.10  
  Purchase #6 $227.82   7.453%   $244.7994   $244.80   $244.80   $244.80  
  Purchase #7 $213.94   10.585%   $236.5855   $236.59   $236.60   $236.60  
  7 purchase totals = $1,240.14       $1,341.7731   $1,341.78   $1,341.80   $1,341.80