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 $86.65   5.318%   $91.258   $91.26   $91.25   $91.30  
  Purchase #2 $21.86   5.697%   $23.1054   $23.11   $23.10   $23.10  
  Purchase #3 $200.62   8.555%   $217.783   $217.78   $217.80   $217.80  
  Purchase #4 $195.90   5.233%   $206.1514   $206.15   $206.15   $206.20  
  Purchase #5 $212.80   6.628%   $226.9044   $226.90   $226.90   $226.90  
  Purchase #6 $219.68   11.611%   $245.187   $245.19   $245.20   $245.20  
  Purchase #7 $175.72   11.492%   $195.9137   $195.91   $195.90   $195.90  
  7 purchase totals = $1,113.23       $1,206.3029   $1,206.30   $1,206.30   $1,206.40