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 $202.68   11.281%   $225.5443   $225.54   $225.55   $225.50  
  Purchase #2 $228.34   9.773%   $250.6557   $250.66   $250.65   $250.70  
  Purchase #3 $95.61   13.533%   $108.5489   $108.55   $108.55   $108.50  
  Purchase #4 $111.28   7.721%   $119.8719   $119.87   $119.85   $119.90  
  Purchase #5 $224.37   13.266%   $254.1349   $254.13   $254.15   $254.10  
  Purchase #6 $44.75   3.781%   $46.442   $46.44   $46.45   $46.40  
  Purchase #7 $206.63   3.767%   $214.4138   $214.41   $214.40   $214.40  
  7 purchase totals = $1,113.66       $1,219.6115   $1,219.60   $1,219.60   $1,219.50