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	$146.92	13.185%	$166.2914	$166.29	$166.30	$166.30
Purchase #2	$92.64	7.325%	$99.4259	$99.43	$99.45	$99.40
Purchase #3	$59.68	7.761%	$64.3118	$64.31	$64.30	$64.30
Purchase #4	$97.91	11.354%	$109.0267	$109.03	$109.05	$109.00
Purchase #5	$192.57	11.730%	$215.1585	$215.16	$215.15	$215.20
Purchase #6	$52.35	9.555%	$57.352	$57.35	$57.35	$57.40
Purchase #7	$143.42	9.369%	$156.857	$156.86	$156.85	$156.90
7 purchase totals =	$785.49		$868.4233	$868.43	$868.45	$868.50