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 $222.93   13.262%   $252.495   $252.50   $252.50   $252.50  
  Purchase #2 $168.51   13.690%   $191.579   $191.58   $191.60   $191.60  
  Purchase #3 $128.58   11.723%   $143.6534   $143.65   $143.65   $143.70  
  Purchase #4 $233.49   10.840%   $258.8003   $258.80   $258.80   $258.80  
  Purchase #5 $237.54   5.250%   $250.0109   $250.01   $250.00   $250.00  
  Purchase #6 $78.48   13.651%   $89.1933   $89.19   $89.20   $89.20  
  Purchase #7 $162.50   11.846%   $181.7498   $181.75   $181.75   $181.70  
  7 purchase totals = $1,232.03       $1,367.4817   $1,367.48   $1,367.50   $1,367.50