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	$84.75	5.789%	$89.6562	$89.66	$89.65	$89.70
Purchase #2	$20.43	9.104%	$22.2899	$22.29	$22.30	$22.30
Purchase #3	$21.30	5.240%	$22.4161	$22.42	$22.40	$22.40
Purchase #4	$108.48	4.543%	$113.4082	$113.41	$113.40	$113.40
Purchase #5	$45.28	4.783%	$47.4457	$47.45	$47.45	$47.40
Purchase #6	$132.54	3.597%	$137.3075	$137.31	$137.30	$137.30
Purchase #7	$167.91	6.626%	$179.0357	$179.04	$179.05	$179.00
7 purchase totals =	$580.69		$611.5593	$611.58	$611.55	$611.50