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 $199.65   13.470%   $226.5429   $226.54   $226.55   $226.50  
  Purchase #2 $96.68   8.371%   $104.7731   $104.77   $104.75   $104.80  
  Purchase #3 $170.61   9.640%   $187.0568   $187.06   $187.05   $187.10  
  Purchase #4 $233.43   7.469%   $250.8649   $250.86   $250.85   $250.90  
  Purchase #5 $26.61   11.787%   $29.7465   $29.75   $29.75   $29.70  
  Purchase #6 $15.53   9.783%   $17.0493   $17.05   $17.05   $17.00  
  Purchase #7 $243.55   11.117%   $270.6255   $270.63   $270.65   $270.60  
  7 purchase totals = $986.06       $1,086.6590   $1,086.66   $1,086.65   $1,086.60