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 $75.76   9.313%   $82.8155   $82.82   $82.80   $82.80  
  Purchase #2 $195.69   8.434%   $212.1945   $212.19   $212.20   $212.20  
  Purchase #3 $71.93   9.351%   $78.6562   $78.66   $78.65   $78.70  
  Purchase #4 $93.41   11.406%   $104.0643   $104.06   $104.05   $104.10  
  Purchase #5 $6.32   3.454%   $6.5383   $6.54   $6.55   $6.50  
  Purchase #6 $50.71   5.161%   $53.3271   $53.33   $53.35   $53.30  
  Purchase #7 $232.64   7.753%   $250.6766   $250.68   $250.70   $250.70  
  7 purchase totals = $726.46       $788.2725   $788.28   $788.30   $788.30