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	$87.78	4.664%	$91.8741	$91.87	$91.85	$91.90
Purchase #2	$233.47	4.647%	$244.3194	$244.32	$244.30	$244.30
Purchase #3	$136.72	7.720%	$147.2748	$147.27	$147.25	$147.30
Purchase #4	$233.66	3.217%	$241.1768	$241.18	$241.20	$241.20
Purchase #5	$134.47	12.238%	$150.9264	$150.93	$150.95	$150.90
Purchase #6	$32.92	9.313%	$35.9858	$35.99	$36.00	$36.00
Purchase #7	$62.54	7.285%	$67.096	$67.10	$67.10	$67.10
7 purchase totals =	$921.56		$978.6533	$978.66	$978.65	$978.70