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	$132.68	8.455%	$143.8981	$143.90	$143.90	$143.90
Purchase #2	$106.30	5.182%	$111.8085	$111.81	$111.80	$111.80
Purchase #3	$50.44	11.621%	$56.3016	$56.30	$56.30	$56.30
Purchase #4	$159.99	4.590%	$167.3335	$167.33	$167.35	$167.30
Purchase #5	$198.78	10.497%	$219.6459	$219.65	$219.65	$219.60
Purchase #6	$112.53	9.399%	$123.1067	$123.11	$123.10	$123.10
Purchase #7	$89.60	9.454%	$98.0708	$98.07	$98.05	$98.10
7 purchase totals =	$850.32		$920.1651	$920.17	$920.15	$920.10