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 $128.48   8.419%   $139.2967   $139.30   $139.30   $139.30  
  Purchase #2 $169.99   12.343%   $190.9719   $190.97   $190.95   $191.00  
  Purchase #3 $38.67   13.421%   $43.8599   $43.86   $43.85   $43.90  
  Purchase #4 $186.68   12.585%   $210.1737   $210.17   $210.15   $210.20  
  Purchase #5 $119.62   6.213%   $127.052   $127.05   $127.05   $127.10  
  Purchase #6 $233.54   12.316%   $262.3028   $262.30   $262.30   $262.30  
  Purchase #7 $178.44   9.687%   $195.7255   $195.73   $195.75   $195.70  
  7 purchase totals = $1,055.42       $1,169.3825   $1,169.38   $1,169.35   $1,169.50