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 $198.96   8.397%   $215.6667   $215.67   $215.65   $215.70  
  Purchase #2 $94.63   8.847%   $103.0019   $103.00   $103.00   $103.00  
  Purchase #3 $210.99   3.840%   $219.092   $219.09   $219.10   $219.10  
  Purchase #4 $169.78   10.546%   $187.685   $187.69   $187.70   $187.70  
  Purchase #5 $107.55   11.495%   $119.9129   $119.91   $119.90   $119.90  
  Purchase #6 $212.41   12.779%   $239.5539   $239.55   $239.55   $239.60  
  Purchase #7 $167.40   13.327%   $189.7094   $189.71   $189.70   $189.70  
  7 purchase totals = $1,161.72       $1,274.6218   $1,274.62   $1,274.60   $1,274.70