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 $206.78   13.196%   $234.0667   $234.07   $234.05   $234.10  
  Purchase #2 $233.68   4.436%   $244.046   $244.05   $244.05   $244.00  
  Purchase #3 $148.41   3.457%   $153.5405   $153.54   $153.55   $153.50  
  Purchase #4 $120.92   3.121%   $124.6939   $124.69   $124.70   $124.70  
  Purchase #5 $242.93   13.468%   $275.6478   $275.65   $275.65   $275.60  
  Purchase #6 $139.62   13.158%   $157.9912   $157.99   $158.00   $158.00  
  Purchase #7 $151.95   3.313%   $156.9841   $156.98   $157.00   $157.00  
  7 purchase totals = $1,244.29       $1,346.9702   $1,346.97   $1,347.00   $1,346.90