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	$60.42	8.662%	$65.6536	$65.65	$65.65	$65.70
Purchase #2	$120.32	10.675%	$133.1642	$133.16	$133.15	$133.20
Purchase #3	$65.75	9.562%	$72.037	$72.04	$72.05	$72.00
Purchase #4	$227.81	11.592%	$254.2177	$254.22	$254.20	$254.20
Purchase #5	$86.44	4.682%	$90.4871	$90.49	$90.50	$90.50
Purchase #6	$86.29	6.317%	$91.7409	$91.74	$91.75	$91.70
Purchase #7	$118.43	10.640%	$131.031	$131.03	$131.05	$131.00
7 purchase totals =	$765.46		$838.3315	$838.33	$838.35	$838.30