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	$87.82	3.533%	$90.9227	$90.92	$90.90	$90.90
Purchase #2	$81.63	7.792%	$87.9906	$87.99	$88.00	$88.00
Purchase #3	$165.37	4.850%	$173.3904	$173.39	$173.40	$173.40
Purchase #4	$145.45	5.399%	$153.3028	$153.30	$153.30	$153.30
Purchase #5	$246.40	3.734%	$255.6006	$255.60	$255.60	$255.60
Purchase #6	$126.47	8.537%	$137.2667	$137.27	$137.25	$137.30
Purchase #7	$71.82	9.591%	$78.7083	$78.71	$78.70	$78.70
7 purchase totals =	$924.96		$977.1821	$977.18	$977.15	$977.20