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	$145.30	6.346%	$154.5207	$154.52	$154.50	$154.50
Purchase #2	$87.77	7.298%	$94.1755	$94.18	$94.20	$94.20
Purchase #3	$237.76	9.108%	$259.4152	$259.42	$259.40	$259.40
Purchase #4	$43.44	4.238%	$45.281	$45.28	$45.30	$45.30
Purchase #5	$75.68	8.688%	$82.2551	$82.26	$82.25	$82.30
Purchase #6	$20.30	4.759%	$21.2661	$21.27	$21.25	$21.30
Purchase #7	$222.42	9.870%	$244.3729	$244.37	$244.35	$244.40
7 purchase totals =	$832.67		$901.2865	$901.30	$901.25	$901.40