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	$132.85	7.236%	$142.463	$142.46	$142.45	$142.50
Purchase #2	$78.74	8.281%	$85.2605	$85.26	$85.25	$85.30
Purchase #3	$73.30	9.789%	$80.4753	$80.48	$80.50	$80.50
Purchase #4	$126.27	10.693%	$139.7721	$139.77	$139.75	$139.80
Purchase #5	$47.52	4.712%	$49.7591	$49.76	$49.75	$49.80
Purchase #6	$54.45	9.247%	$59.485	$59.49	$59.50	$59.50
Purchase #7	$208.60	11.190%	$231.9423	$231.94	$231.95	$231.90
7 purchase totals =	$721.73		$789.1573	$789.16	$789.15	$789.30