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	$164.49	12.697%	$185.3753	$185.38	$185.40	$185.40
Purchase #2	$153.28	9.760%	$168.2401	$168.24	$168.25	$168.20
Purchase #3	$52.51	10.297%	$57.917	$57.92	$57.90	$57.90
Purchase #4	$165.62	11.802%	$185.1665	$185.17	$185.15	$185.20
Purchase #5	$55.64	10.694%	$61.5901	$61.59	$61.60	$61.60
Purchase #6	$55.66	5.802%	$58.8894	$58.89	$58.90	$58.90
Purchase #7	$119.51	3.410%	$123.5853	$123.59	$123.60	$123.60
7 purchase totals =	$766.71		$840.7637	$840.78	$840.80	$840.80