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 $83.85   13.667%   $95.3098   $95.31   $95.30   $95.30  
  Purchase #2 $232.50   7.359%   $249.6097   $249.61   $249.60   $249.60  
  Purchase #3 $228.62   8.851%   $248.8552   $248.86   $248.85   $248.90  
  Purchase #4 $73.69   12.486%   $82.8909   $82.89   $82.90   $82.90  
  Purchase #5 $26.94   4.643%   $28.1908   $28.19   $28.20   $28.20  
  Purchase #6 $153.86   10.561%   $170.1092   $170.11   $170.10   $170.10  
  Purchase #7 $231.55   5.465%   $244.2042   $244.20   $244.20   $244.20  
  7 purchase totals = $1,031.01       $1,119.1698   $1,119.17   $1,119.15   $1,119.20