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	$53.32	11.636%	$59.5243	$59.52	$59.50	$59.50
Purchase #2	$62.42	13.387%	$70.7762	$70.78	$70.80	$70.80
Purchase #3	$225.34	10.444%	$248.8745	$248.87	$248.85	$248.90
Purchase #4	$83.56	5.470%	$88.1307	$88.13	$88.15	$88.10
Purchase #5	$220.57	12.615%	$248.3949	$248.39	$248.40	$248.40
Purchase #6	$146.33	3.251%	$151.0872	$151.09	$151.10	$151.10
Purchase #7	$22.94	11.144%	$25.4964	$25.50	$25.50	$25.50
7 purchase totals =	$814.48		$892.2842	$892.28	$892.30	$892.30