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 $191.60   7.591%   $206.1444   $206.14   $206.15   $206.10  
  Purchase #2 $144.67   13.845%   $164.6996   $164.70   $164.70   $164.70  
  Purchase #3 $187.42   12.245%   $210.3696   $210.37   $210.35   $210.40  
  Purchase #4 $249.87   10.388%   $275.8265   $275.83   $275.85   $275.80  
  Purchase #5 $198.98   8.482%   $215.8575   $215.86   $215.85   $215.90  
  Purchase #6 $238.77   9.837%   $262.2578   $262.26   $262.25   $262.30  
  Purchase #7 $65.33   8.552%   $70.917   $70.92   $70.90   $70.90  
  7 purchase totals = $1,276.64       $1,406.0724   $1,406.08   $1,406.05   $1,406.10