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	$74.33	12.773%	$83.8242	$83.82	$83.80	$83.80
Purchase #2	$56.39	6.513%	$60.0627	$60.06	$60.05	$60.10
Purchase #3	$153.28	9.285%	$167.512	$167.51	$167.50	$167.50
Purchase #4	$175.48	7.778%	$189.1288	$189.13	$189.15	$189.10
Purchase #5	$93.56	3.430%	$96.7691	$96.77	$96.75	$96.80
Purchase #6	$81.33	10.185%	$89.6135	$89.61	$89.60	$89.60
Purchase #7	$158.49	13.737%	$180.2618	$180.26	$180.25	$180.30
7 purchase totals =	$792.86		$867.1721	$867.16	$867.10	$867.20