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 $30.81   5.146%   $32.3955   $32.40   $32.40   $32.40  
  Purchase #2 $201.59   13.427%   $228.6575   $228.66   $228.65   $228.70  
  Purchase #3 $53.77   12.331%   $60.4004   $60.40   $60.40   $60.40  
  Purchase #4 $187.66   12.451%   $211.0255   $211.03   $211.05   $211.00  
  Purchase #5 $202.47   6.693%   $216.0213   $216.02   $216.00   $216.00  
  Purchase #6 $90.36   8.428%   $97.9755   $97.98   $98.00   $98.00  
  Purchase #7 $162.49   11.701%   $181.503   $181.50   $181.50   $181.50  
  7 purchase totals = $929.15       $1,027.9787   $1,027.99   $1,028.00   $1,028.00