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	$109.43	10.474%	$120.8917	$120.89	$120.90	$120.90
Purchase #2	$17.50	5.281%	$18.4242	$18.42	$18.40	$18.40
Purchase #3	$200.42	12.347%	$225.1659	$225.17	$225.15	$225.20
Purchase #4	$157.41	7.631%	$169.422	$169.42	$169.40	$169.40
Purchase #5	$29.36	13.218%	$33.2408	$33.24	$33.25	$33.20
Purchase #6	$231.57	12.243%	$259.9211	$259.92	$259.90	$259.90
Purchase #7	$74.83	10.273%	$82.5173	$82.52	$82.50	$82.50
7 purchase totals =	$820.52		$909.5830	$909.58	$909.50	$909.50