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 $192.35   13.866%   $219.0213   $219.02   $219.00   $219.00  
  Purchase #2 $90.93   7.787%   $98.0107   $98.01   $98.00   $98.00  
  Purchase #3 $218.43   6.739%   $233.15   $233.15   $233.15   $233.20  
  Purchase #4 $62.82   11.314%   $69.9275   $69.93   $69.95   $69.90  
  Purchase #5 $31.60   13.584%   $35.8925   $35.89   $35.90   $35.90  
  Purchase #6 $234.70   4.797%   $245.9586   $245.96   $245.95   $246.00  
  Purchase #7 $208.36   13.336%   $236.1469   $236.15   $236.15   $236.10  
  7 purchase totals = $1,039.19       $1,138.1075   $1,138.11   $1,138.10   $1,138.10