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	$226.54	10.698%	$250.7752	$250.78	$250.80	$250.80
Purchase #2	$132.51	9.508%	$145.1091	$145.11	$145.10	$145.10
Purchase #3	$50.44	12.857%	$56.9251	$56.93	$56.95	$56.90
Purchase #4	$249.77	8.687%	$271.4675	$271.47	$271.45	$271.50
Purchase #5	$195.46	5.335%	$205.8878	$205.89	$205.90	$205.90
Purchase #6	$218.57	10.111%	$240.6696	$240.67	$240.65	$240.70
Purchase #7	$189.33	6.107%	$200.8924	$200.89	$200.90	$200.90
7 purchase totals =	$1,262.62		$1,371.7267	$1,371.74	$1,371.75	$1,371.80