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	$132.81	8.736%	$144.4123	$144.41	$144.40	$144.40
Purchase #2	$120.85	8.823%	$131.5126	$131.51	$131.50	$131.50
Purchase #3	$241.31	11.505%	$269.0727	$269.07	$269.05	$269.10
Purchase #4	$27.78	9.435%	$30.401	$30.40	$30.40	$30.40
Purchase #5	$99.70	12.150%	$111.8136	$111.81	$111.80	$111.80
Purchase #6	$16.50	11.633%	$18.4194	$18.42	$18.40	$18.40
Purchase #7	$16.34	13.658%	$18.5717	$18.57	$18.55	$18.60
7 purchase totals =	$655.29		$724.2033	$724.19	$724.10	$724.20