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	6.139%	$162.2016	$162.20	$162.20	$162.20
Purchase #2	$17.89	11.677%	$19.979	$19.98	$20.00	$20.00
Purchase #3	$43.67	6.476%	$46.4981	$46.50	$46.50	$46.50
Purchase #4	$82.89	5.281%	$87.2674	$87.27	$87.25	$87.30
Purchase #5	$35.77	5.717%	$37.815	$37.82	$37.80	$37.80
Purchase #6	$55.26	11.816%	$61.7895	$61.79	$61.80	$61.80
Purchase #7	$215.37	3.381%	$222.6517	$222.65	$222.65	$222.70
7 purchase totals =	$603.67		$638.2023	$638.21	$638.20	$638.30