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	$40.89	10.145%	$45.0383	$45.04	$45.05	$45.00
Purchase #2	$124.64	12.463%	$140.1739	$140.17	$140.15	$140.20
Purchase #3	$13.55	7.550%	$14.573	$14.57	$14.55	$14.60
Purchase #4	$30.71	10.221%	$33.8489	$33.85	$33.85	$33.80
Purchase #5	$116.74	9.546%	$127.884	$127.88	$127.90	$127.90
Purchase #6	$183.28	12.569%	$206.3165	$206.32	$206.30	$206.30
Purchase #7	$207.83	8.624%	$225.7533	$225.75	$225.75	$225.80
7 purchase totals =	$717.64		$793.5879	$793.58	$793.55	$793.60