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 $109.56   6.554%   $116.7406   $116.74   $116.75   $116.70  
  Purchase #2 $215.64   13.447%   $244.6371   $244.64   $244.65   $244.60  
  Purchase #3 $212.88   6.153%   $225.9785   $225.98   $226.00   $226.00  
  Purchase #4 $185.89   12.213%   $208.5927   $208.59   $208.60   $208.60  
  Purchase #5 $233.97   4.336%   $244.1149   $244.11   $244.10   $244.10  
  Purchase #6 $199.43   9.763%   $218.9004   $218.90   $218.90   $218.90  
  Purchase #7 $16.95   3.321%   $17.5129   $17.51   $17.50   $17.50  
  7 purchase totals = $1,174.32       $1,276.4771   $1,276.47   $1,276.50   $1,276.40