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	$16.84	10.595%	$18.6242	$18.62	$18.60	$18.60
Purchase #2	$63.88	13.136%	$72.2713	$72.27	$72.25	$72.30
Purchase #3	$128.71	12.581%	$144.903	$144.90	$144.90	$144.90
Purchase #4	$53.30	13.287%	$60.382	$60.38	$60.40	$60.40
Purchase #5	$61.64	10.869%	$68.3397	$68.34	$68.35	$68.30
Purchase #6	$75.55	8.693%	$82.1176	$82.12	$82.10	$82.10
Purchase #7	$152.40	8.327%	$165.0903	$165.09	$165.10	$165.10
7 purchase totals =	$552.32		$611.7281	$611.72	$611.70	$611.70