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 $84.65   9.321%   $92.5402   $92.54   $92.55   $92.50  
  Purchase #2 $118.46   6.193%   $125.7962   $125.80   $125.80   $125.80  
  Purchase #3 $23.71   12.588%   $26.6946   $26.69   $26.70   $26.70  
  Purchase #4 $185.37   10.430%   $204.7041   $204.70   $204.70   $204.70  
  Purchase #5 $169.97   6.805%   $181.5365   $181.54   $181.55   $181.50  
  Purchase #6 $214.85   13.741%   $244.3725   $244.37   $244.35   $244.40  
  Purchase #7 $49.32   10.676%   $54.5854   $54.59   $54.60   $54.60  
  7 purchase totals = $846.33       $930.2295   $930.23   $930.25   $930.20