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 $34.30   5.725%   $36.2637   $36.26   $36.25   $36.30  
  Purchase #2 $206.48   12.188%   $231.6458   $231.65   $231.65   $231.60  
  Purchase #3 $84.86   6.757%   $90.594   $90.59   $90.60   $90.60  
  Purchase #4 $218.64   7.646%   $235.3572   $235.36   $235.35   $235.40  
  Purchase #5 $99.81   10.411%   $110.2012   $110.20   $110.20   $110.20  
  Purchase #6 $73.85   6.388%   $78.5675   $78.57   $78.55   $78.60  
  Purchase #7 $33.79   10.515%   $37.343   $37.34   $37.35   $37.30  
  7 purchase totals = $751.73       $819.9724   $819.97   $819.95   $820.00