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	$201.66	11.242%	$224.3306	$224.33	$224.35	$224.30
Purchase #2	$247.88	11.704%	$276.8919	$276.89	$276.90	$276.90
Purchase #3	$78.71	13.458%	$89.3028	$89.30	$89.30	$89.30
Purchase #4	$127.27	3.451%	$131.6621	$131.66	$131.65	$131.70
Purchase #5	$145.26	4.470%	$151.7531	$151.75	$151.75	$151.80
Purchase #6	$51.38	3.207%	$53.0278	$53.03	$53.05	$53.00
Purchase #7	$200.30	6.180%	$212.6785	$212.68	$212.70	$212.70
7 purchase totals =	$1,052.46		$1,139.6468	$1,139.64	$1,139.70	$1,139.70