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 $239.80   8.825%   $260.9624   $260.96   $260.95   $261.00  
  Purchase #2 $96.49   6.749%   $103.0021   $103.00   $103.00   $103.00  
  Purchase #3 $196.96   8.163%   $213.0378   $213.04   $213.05   $213.00  
  Purchase #4 $227.62   10.862%   $252.3441   $252.34   $252.35   $252.30  
  Purchase #5 $170.85   13.781%   $194.3948   $194.39   $194.40   $194.40  
  Purchase #6 $145.46   4.487%   $151.9868   $151.99   $152.00   $152.00  
  Purchase #7 $244.55   8.121%   $264.4099   $264.41   $264.40   $264.40  
  7 purchase totals = $1,321.73       $1,440.1379   $1,440.13   $1,440.15   $1,440.10