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 $29.97   11.664%   $33.4657   $33.47   $33.45   $33.50  
  Purchase #2 $183.26   11.515%   $204.3624   $204.36   $204.35   $204.40  
  Purchase #3 $51.37   8.590%   $55.7827   $55.78   $55.80   $55.80  
  Purchase #4 $113.90   10.682%   $126.0668   $126.07   $126.05   $126.10  
  Purchase #5 $113.90   4.832%   $119.4036   $119.40   $119.40   $119.40  
  Purchase #6 $175.96   6.606%   $187.5839   $187.58   $187.60   $187.60  
  Purchase #7 $217.93   5.813%   $230.5983   $230.60   $230.60   $230.60  
  7 purchase totals = $886.29       $957.2634   $957.26   $957.25   $957.40