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	$123.25	3.142%	$127.1225	$127.12	$127.10	$127.10
Purchase #2	$30.76	12.240%	$34.525	$34.53	$34.55	$34.50
Purchase #3	$230.52	12.796%	$260.0173	$260.02	$260.00	$260.00
Purchase #4	$141.53	7.643%	$152.3471	$152.35	$152.35	$152.30
Purchase #5	$102.41	10.707%	$113.375	$113.38	$113.40	$113.40
Purchase #6	$101.54	9.863%	$111.5549	$111.55	$111.55	$111.60
Purchase #7	$37.94	7.331%	$40.7214	$40.72	$40.70	$40.70
7 purchase totals =	$767.95		$839.6632	$839.67	$839.65	$839.60