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	$93.72	6.311%	$99.6347	$99.63	$99.65	$99.60
Purchase #2	$49.98	5.707%	$52.8324	$52.83	$52.85	$52.80
Purchase #3	$75.94	10.836%	$84.1689	$84.17	$84.15	$84.20
Purchase #4	$161.29	4.107%	$167.9142	$167.91	$167.90	$167.90
Purchase #5	$188.73	13.602%	$214.4011	$214.40	$214.40	$214.40
Purchase #6	$93.50	7.374%	$100.3947	$100.39	$100.40	$100.40
Purchase #7	$100.40	3.761%	$104.176	$104.18	$104.20	$104.20
7 purchase totals =	$763.56		$823.5220	$823.51	$823.55	$823.50