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	$74.27	6.336%	$78.9757	$78.98	$79.00	$79.00
Purchase #2	$131.82	9.163%	$143.8987	$143.90	$143.90	$143.90
Purchase #3	$135.58	12.462%	$152.476	$152.48	$152.50	$152.50
Purchase #4	$71.67	9.346%	$78.3683	$78.37	$78.35	$78.40
Purchase #5	$14.46	4.433%	$15.101	$15.10	$15.10	$15.10
Purchase #6	$230.33	3.127%	$237.5324	$237.53	$237.55	$237.50
Purchase #7	$155.56	6.563%	$165.7694	$165.77	$165.75	$165.80
7 purchase totals =	$813.69		$872.1215	$872.13	$872.15	$872.20