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	$91.50	9.203%	$99.9207	$99.92	$99.90	$99.90
Purchase #2	$95.32	9.716%	$104.5813	$104.58	$104.60	$104.60
Purchase #3	$159.77	4.157%	$166.4116	$166.41	$166.40	$166.40
Purchase #4	$5.76	7.166%	$6.1728	$6.17	$6.15	$6.20
Purchase #5	$91.73	13.185%	$103.8246	$103.82	$103.80	$103.80
Purchase #6	$59.56	6.155%	$63.2259	$63.23	$63.25	$63.20
Purchase #7	$45.94	12.143%	$51.5185	$51.52	$51.50	$51.50
7 purchase totals =	$549.58		$595.6554	$595.65	$595.60	$595.60