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 $193.64   13.766%   $220.2965   $220.30   $220.30   $220.30  
  Purchase #2 $199.74   9.813%   $219.3405   $219.34   $219.35   $219.30  
  Purchase #3 $19.91   8.641%   $21.6304   $21.63   $21.65   $21.60  
  Purchase #4 $226.94   9.842%   $249.2754   $249.28   $249.30   $249.30  
  Purchase #5 $73.56   11.820%   $82.2548   $82.25   $82.25   $82.30  
  Purchase #6 $136.65   3.401%   $141.2975   $141.30   $141.30   $141.30  
  Purchase #7 $52.53   8.520%   $57.0056   $57.01   $57.00   $57.00  
  7 purchase totals = $902.97       $991.1007   $991.11   $991.15   $991.10