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	$69.53	13.162%	$78.6815	$78.68	$78.70	$78.70
Purchase #2	$129.50	10.608%	$143.2374	$143.24	$143.25	$143.20
Purchase #3	$28.98	12.141%	$32.4985	$32.50	$32.50	$32.50
Purchase #4	$110.66	3.780%	$114.8429	$114.84	$114.85	$114.80
Purchase #5	$165.54	10.810%	$183.4349	$183.43	$183.45	$183.40
Purchase #6	$197.29	12.399%	$221.752	$221.75	$221.75	$221.80
Purchase #7	$68.59	13.780%	$78.0417	$78.04	$78.05	$78.00
7 purchase totals =	$770.09		$852.4889	$852.48	$852.55	$852.40