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	$28.85	9.274%	$31.5255	$31.53	$31.55	$31.50
Purchase #2	$199.93	13.784%	$227.4884	$227.49	$227.50	$227.50
Purchase #3	$132.76	12.701%	$149.6218	$149.62	$149.60	$149.60
Purchase #4	$216.45	11.408%	$241.1426	$241.14	$241.15	$241.10
Purchase #5	$136.51	5.529%	$144.0576	$144.06	$144.05	$144.10
Purchase #6	$198.33	8.814%	$215.8108	$215.81	$215.80	$215.80
Purchase #7	$91.80	11.289%	$102.1633	$102.16	$102.15	$102.20
7 purchase totals =	$1,004.63		$1,111.8100	$1,111.81	$1,111.80	$1,111.80