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 $118.63   13.296%   $134.403   $134.40   $134.40   $134.40  
  Purchase #2 $96.28   11.222%   $107.0845   $107.08   $107.10   $107.10  
  Purchase #3 $31.69   8.384%   $34.3469   $34.35   $34.35   $34.30  
  Purchase #4 $234.81   4.399%   $245.1393   $245.14   $245.15   $245.10  
  Purchase #5 $237.51   7.154%   $254.5015   $254.50   $254.50   $254.50  
  Purchase #6 $224.25   7.523%   $241.1203   $241.12   $241.10   $241.10  
  Purchase #7 $90.56   13.757%   $103.0183   $103.02   $103.00   $103.00  
  7 purchase totals = $1,033.73       $1,119.6138   $1,119.61   $1,119.60   $1,119.50