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 $75.68   9.154%   $82.6077   $82.61   $82.60   $82.60  
  Purchase #2 $96.69   12.836%   $109.1011   $109.10   $109.10   $109.10  
  Purchase #3 $89.29   5.620%   $94.3081   $94.31   $94.30   $94.30  
  Purchase #4 $76.84   12.547%   $86.4811   $86.48   $86.50   $86.50  
  Purchase #5 $155.40   10.653%   $171.9548   $171.95   $171.95   $172.00  
  Purchase #6 $110.81   13.620%   $125.9023   $125.90   $125.90   $125.90  
  Purchase #7 $130.76   4.340%   $136.435   $136.44   $136.45   $136.40  
  7 purchase totals = $735.47       $806.7901   $806.79   $806.80   $806.80