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 $54.93   8.464%   $59.5793   $59.58   $59.60   $59.60  
  Purchase #2 $205.91   13.509%   $233.7264   $233.73   $233.75   $233.70  
  Purchase #3 $185.49   5.343%   $195.4007   $195.40   $195.40   $195.40  
  Purchase #4 $218.64   3.841%   $227.038   $227.04   $227.05   $227.00  
  Purchase #5 $68.28   7.411%   $73.3402   $73.34   $73.35   $73.30  
  Purchase #6 $237.35   4.175%   $247.2594   $247.26   $247.25   $247.30  
  Purchase #7 $108.53   10.737%   $120.1829   $120.18   $120.20   $120.20  
  7 purchase totals = $1,079.13       $1,156.5269   $1,156.53   $1,156.60   $1,156.50