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 $61.79   8.286%   $66.9099   $66.91   $66.90   $66.90  
  Purchase #2 $167.99   4.577%   $175.6789   $175.68   $175.70   $175.70  
  Purchase #3 $176.32   8.179%   $190.7412   $190.74   $190.75   $190.70  
  Purchase #4 $214.55   8.319%   $232.3984   $232.40   $232.40   $232.40  
  Purchase #5 $29.34   9.509%   $32.1299   $32.13   $32.15   $32.10  
  Purchase #6 $88.60   4.796%   $92.8493   $92.85   $92.85   $92.80  
  Purchase #7 $130.98   9.352%   $143.2292   $143.23   $143.25   $143.20  
  7 purchase totals = $869.57       $933.9368   $933.94   $934.00   $933.80