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	$193.91	13.567%	$220.2178	$220.22	$220.20	$220.20
Purchase #2	$12.78	5.241%	$13.4498	$13.45	$13.45	$13.40
Purchase #3	$105.33	11.767%	$117.7242	$117.72	$117.70	$117.70
Purchase #4	$212.39	8.133%	$229.6637	$229.66	$229.65	$229.70
Purchase #5	$70.85	10.793%	$78.4968	$78.50	$78.50	$78.50
Purchase #6	$72.89	10.745%	$80.722	$80.72	$80.70	$80.70
Purchase #7	$45.28	11.806%	$50.6258	$50.63	$50.65	$50.60
7 purchase totals =	$713.43		$790.9001	$790.90	$790.85	$790.80