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	$36.62	4.190%	$38.1544	$38.15	$38.15	$38.20
Purchase #2	$36.94	9.811%	$40.5642	$40.56	$40.55	$40.60
Purchase #3	$217.36	3.269%	$224.4655	$224.47	$224.45	$224.50
Purchase #4	$163.28	5.261%	$171.8702	$171.87	$171.85	$171.90
Purchase #5	$57.93	11.841%	$64.7895	$64.79	$64.80	$64.80
Purchase #6	$28.96	12.288%	$32.5186	$32.52	$32.50	$32.50
Purchase #7	$223.51	8.632%	$242.8034	$242.80	$242.80	$242.80
7 purchase totals =	$764.60		$815.1658	$815.16	$815.10	$815.30