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	$96.70	4.357%	$100.9132	$100.91	$100.90	$100.90
Purchase #2	$39.89	9.462%	$43.6644	$43.66	$43.65	$43.70
Purchase #3	$100.31	9.434%	$109.7732	$109.77	$109.75	$109.80
Purchase #4	$236.99	4.470%	$247.5835	$247.58	$247.60	$247.60
Purchase #5	$131.27	11.704%	$146.6338	$146.63	$146.65	$146.60
Purchase #6	$79.63	8.109%	$86.0872	$86.09	$86.10	$86.10
Purchase #7	$149.88	9.468%	$164.0706	$164.07	$164.05	$164.10
7 purchase totals =	$834.67		$898.7259	$898.71	$898.70	$898.80