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 $241.47   11.702%   $269.7268   $269.73   $269.75   $269.70  
  Purchase #2 $39.79   10.796%   $44.0857   $44.09   $44.10   $44.10  
  Purchase #3 $146.99   7.552%   $158.0907   $158.09   $158.10   $158.10  
  Purchase #4 $95.44   6.612%   $101.7505   $101.75   $101.75   $101.80  
  Purchase #5 $194.85   13.161%   $220.4942   $220.49   $220.50   $220.50  
  Purchase #6 $199.35   11.504%   $222.2832   $222.28   $222.30   $222.30  
  Purchase #7 $216.78   8.868%   $236.0041   $236.00   $236.00   $236.00  
  7 purchase totals = $1,134.67       $1,252.4352   $1,252.43   $1,252.50   $1,252.50