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	$167.30	12.515%	$188.2376	$188.24	$188.25	$188.20
Purchase #2	$103.78	13.569%	$117.8619	$117.86	$117.85	$117.90
Purchase #3	$50.76	11.245%	$56.468	$56.47	$56.45	$56.50
Purchase #4	$207.63	7.428%	$223.0528	$223.05	$223.05	$223.10
Purchase #5	$228.25	3.769%	$236.8527	$236.85	$236.85	$236.90
Purchase #6	$99.56	5.838%	$105.3723	$105.37	$105.35	$105.40
Purchase #7	$56.61	12.472%	$63.6704	$63.67	$63.65	$63.70
7 purchase totals =	$913.89		$991.5157	$991.51	$991.45	$991.70