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	$152.82	13.292%	$173.1328	$173.13	$173.15	$173.10
Purchase #2	$152.93	4.152%	$159.2797	$159.28	$159.30	$159.30
Purchase #3	$177.91	6.732%	$189.8869	$189.89	$189.90	$189.90
Purchase #4	$123.95	9.131%	$135.2679	$135.27	$135.25	$135.30
Purchase #5	$116.52	13.164%	$131.8587	$131.86	$131.85	$131.90
Purchase #6	$227.96	10.501%	$251.8981	$251.90	$251.90	$251.90
Purchase #7	$220.66	12.507%	$248.2579	$248.26	$248.25	$248.30
7 purchase totals =	$1,172.75		$1,289.5820	$1,289.59	$1,289.60	$1,289.70