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	$218.50	9.376%	$238.9866	$238.99	$239.00	$239.00
Purchase #2	$175.36	7.547%	$188.5944	$188.59	$188.60	$188.60
Purchase #3	$181.33	3.623%	$187.8996	$187.90	$187.90	$187.90
Purchase #4	$85.28	3.793%	$88.5147	$88.51	$88.50	$88.50
Purchase #5	$148.68	7.343%	$159.5976	$159.60	$159.60	$159.60
Purchase #6	$72.50	13.174%	$82.0512	$82.05	$82.05	$82.10
Purchase #7	$134.56	12.361%	$151.193	$151.19	$151.20	$151.20
7 purchase totals =	$1,016.21		$1,096.8371	$1,096.83	$1,096.85	$1,096.90