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	$35.69	11.427%	$39.7683	$39.77	$39.75	$39.80
Purchase #2	$212.92	8.414%	$230.8351	$230.84	$230.85	$230.80
Purchase #3	$130.72	4.513%	$136.6194	$136.62	$136.60	$136.60
Purchase #4	$240.83	13.456%	$273.2361	$273.24	$273.25	$273.20
Purchase #5	$111.38	13.558%	$126.4809	$126.48	$126.50	$126.50
Purchase #6	$80.88	10.698%	$89.5325	$89.53	$89.55	$89.50
Purchase #7	$240.47	3.251%	$248.2877	$248.29	$248.30	$248.30
7 purchase totals =	$1,052.89		$1,144.7600	$1,144.77	$1,144.80	$1,144.70