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	$32.78	13.555%	$37.2233	$37.22	$37.20	$37.20
Purchase #2	$240.81	12.803%	$271.6409	$271.64	$271.65	$271.60
Purchase #3	$158.62	8.429%	$171.9901	$171.99	$172.00	$172.00
Purchase #4	$112.40	6.275%	$119.4531	$119.45	$119.45	$119.50
Purchase #5	$63.92	12.461%	$71.8851	$71.89	$71.90	$71.90
Purchase #6	$40.42	4.177%	$42.1083	$42.11	$42.10	$42.10
Purchase #7	$162.84	5.821%	$172.3189	$172.32	$172.30	$172.30
7 purchase totals =	$811.79		$886.6197	$886.62	$886.60	$886.60