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	$127.51	6.830%	$136.2189	$136.22	$136.20	$136.20
Purchase #2	$97.75	7.749%	$105.3246	$105.32	$105.30	$105.30
Purchase #3	$78.76	4.523%	$82.3223	$82.32	$82.30	$82.30
Purchase #4	$7.54	8.798%	$8.2034	$8.20	$8.20	$8.20
Purchase #5	$127.61	10.819%	$141.4161	$141.42	$141.40	$141.40
Purchase #6	$169.54	9.120%	$185.002	$185.00	$185.00	$185.00
Purchase #7	$128.92	13.324%	$146.0973	$146.10	$146.10	$146.10
7 purchase totals =	$737.63		$804.5846	$804.58	$804.50	$804.50