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	$18.90	3.104%	$19.4867	$19.49	$19.50	$19.50
Purchase #2	$185.63	6.530%	$197.7516	$197.75	$197.75	$197.80
Purchase #3	$131.70	12.842%	$148.6129	$148.61	$148.60	$148.60
Purchase #4	$108.97	8.620%	$118.3632	$118.36	$118.35	$118.40
Purchase #5	$80.44	10.808%	$89.134	$89.13	$89.15	$89.10
Purchase #6	$133.66	13.850%	$152.1719	$152.17	$152.15	$152.20
Purchase #7	$38.66	10.278%	$42.6335	$42.63	$42.65	$42.60
7 purchase totals =	$697.96		$768.1538	$768.14	$768.15	$768.20