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	$40.46	12.513%	$45.5228	$45.52	$45.50	$45.50
Purchase #2	$90.46	8.443%	$98.0975	$98.10	$98.10	$98.10
Purchase #3	$111.41	7.579%	$119.8538	$119.85	$119.85	$119.90
Purchase #4	$26.31	8.639%	$28.5829	$28.58	$28.60	$28.60
Purchase #5	$196.32	7.413%	$210.8732	$210.87	$210.85	$210.90
Purchase #6	$222.74	12.306%	$250.1504	$250.15	$250.15	$250.20
Purchase #7	$93.62	9.329%	$102.3538	$102.35	$102.35	$102.40
7 purchase totals =	$781.32		$855.4344	$855.42	$855.40	$855.60