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	$9.69	6.115%	$10.2825	$10.28	$10.30	$10.30
Purchase #2	$40.79	3.851%	$42.3608	$42.36	$42.35	$42.40
Purchase #3	$166.65	11.131%	$185.1998	$185.20	$185.20	$185.20
Purchase #4	$157.88	8.340%	$171.0472	$171.05	$171.05	$171.00
Purchase #5	$45.78	5.872%	$48.4682	$48.47	$48.45	$48.50
Purchase #6	$46.88	3.127%	$48.3459	$48.35	$48.35	$48.30
Purchase #7	$83.87	10.636%	$92.7904	$92.79	$92.80	$92.80
7 purchase totals =	$551.54		$598.4948	$598.50	$598.50	$598.50