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	$28.57	7.479%	$30.7068	$30.71	$30.70	$30.70
Purchase #2	$199.86	5.653%	$211.1581	$211.16	$211.15	$211.20
Purchase #3	$89.91	8.254%	$97.3312	$97.33	$97.35	$97.30
Purchase #4	$85.32	4.385%	$89.0613	$89.06	$89.05	$89.10
Purchase #5	$44.78	7.767%	$48.2581	$48.26	$48.25	$48.30
Purchase #6	$35.94	3.111%	$37.0581	$37.06	$37.05	$37.10
Purchase #7	$147.53	13.448%	$167.3698	$167.37	$167.35	$167.40
7 purchase totals =	$631.91		$680.9434	$680.95	$680.90	$681.10