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	$113.36	12.839%	$127.9143	$127.91	$127.90	$127.90
Purchase #2	$128.33	13.415%	$145.5455	$145.55	$145.55	$145.50
Purchase #3	$127.52	7.531%	$137.1235	$137.12	$137.10	$137.10
Purchase #4	$247.78	6.181%	$263.0953	$263.10	$263.10	$263.10
Purchase #5	$14.91	3.713%	$15.4636	$15.46	$15.45	$15.50
Purchase #6	$91.33	12.142%	$102.4193	$102.42	$102.40	$102.40
Purchase #7	$54.88	7.413%	$58.9483	$58.95	$58.95	$58.90
7 purchase totals =	$778.11		$850.5098	$850.51	$850.45	$850.40