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 $182.27   13.523%   $206.9184   $206.92   $206.90   $206.90  
  Purchase #2 $77.29   13.424%   $87.6654   $87.67   $87.65   $87.70  
  Purchase #3 $151.39   3.468%   $156.6402   $156.64   $156.65   $156.60  
  Purchase #4 $28.31   5.287%   $29.8067   $29.81   $29.80   $29.80  
  Purchase #5 $224.60   13.521%   $254.9682   $254.97   $254.95   $255.00  
  Purchase #6 $13.41   9.187%   $14.642   $14.64   $14.65   $14.60  
  Purchase #7 $98.81   13.300%   $111.9517   $111.95   $111.95   $112.00  
  7 purchase totals = $776.08       $862.5926   $862.60   $862.55   $862.60