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 $78.34   8.769%   $85.2096   $85.21   $85.20   $85.20  
  Purchase #2 $123.45   12.804%   $139.2565   $139.26   $139.25   $139.30  
  Purchase #3 $42.66   3.463%   $44.1373   $44.14   $44.15   $44.10  
  Purchase #4 $198.80   4.237%   $207.2232   $207.22   $207.20   $207.20  
  Purchase #5 $51.48   12.570%   $57.951   $57.95   $57.95   $58.00  
  Purchase #6 $226.93   6.841%   $242.4543   $242.45   $242.45   $242.50  
  Purchase #7 $101.47   7.505%   $109.0853   $109.09   $109.10   $109.10  
  7 purchase totals = $823.13       $885.3172   $885.32   $885.30   $885.40