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	$33.36	11.784%	$37.2911	$37.29	$37.30	$37.30
Purchase #2	$157.36	10.532%	$173.9332	$173.93	$173.95	$173.90
Purchase #3	$55.61	10.773%	$61.6009	$61.60	$61.60	$61.60
Purchase #4	$234.59	3.786%	$243.4716	$243.47	$243.45	$243.50
Purchase #5	$233.45	4.435%	$243.8035	$243.80	$243.80	$243.80
Purchase #6	$109.64	9.121%	$119.6403	$119.64	$119.65	$119.60
Purchase #7	$55.66	11.241%	$61.9167	$61.92	$61.90	$61.90
7 purchase totals =	$879.67		$941.6573	$941.65	$941.65	$941.60