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	$129.87	12.344%	$145.9012	$145.90	$145.90	$145.90
Purchase #2	$118.68	10.650%	$131.3194	$131.32	$131.30	$131.30
Purchase #3	$60.28	12.608%	$67.8801	$67.88	$67.90	$67.90
Purchase #4	$106.96	10.432%	$118.1181	$118.12	$118.10	$118.10
Purchase #5	$138.29	10.689%	$153.0718	$153.07	$153.05	$153.10
Purchase #6	$171.42	11.782%	$191.6167	$191.62	$191.60	$191.60
Purchase #7	$101.64	3.735%	$105.4363	$105.44	$105.45	$105.40
7 purchase totals =	$827.14		$913.3436	$913.35	$913.30	$913.30