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	$148.87	8.438%	$161.4317	$161.43	$161.45	$161.40
Purchase #2	$209.65	13.859%	$238.7054	$238.71	$238.70	$238.70
Purchase #3	$37.35	4.853%	$39.1626	$39.16	$39.15	$39.20
Purchase #4	$80.70	3.397%	$83.4414	$83.44	$83.45	$83.40
Purchase #5	$19.38	7.119%	$20.7597	$20.76	$20.75	$20.80
Purchase #6	$148.93	5.126%	$156.5642	$156.56	$156.55	$156.60
Purchase #7	$123.31	12.826%	$139.1257	$139.13	$139.15	$139.10
7 purchase totals =	$768.19		$839.1907	$839.19	$839.20	$839.20