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	$33.57	11.235%	$37.3416	$37.34	$37.35	$37.30
Purchase #2	$134.86	13.789%	$153.4558	$153.46	$153.45	$153.50
Purchase #3	$197.83	11.152%	$219.892	$219.89	$219.90	$219.90
Purchase #4	$135.48	11.807%	$151.4761	$151.48	$151.50	$151.50
Purchase #5	$248.95	8.384%	$269.822	$269.82	$269.80	$269.80
Purchase #6	$31.51	3.621%	$32.651	$32.65	$32.65	$32.70
Purchase #7	$13.89	11.572%	$15.4974	$15.50	$15.50	$15.50
7 purchase totals =	$796.09		$880.1359	$880.14	$880.15	$880.20