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	$203.95	6.631%	$217.4739	$217.47	$217.45	$217.50
Purchase #2	$58.43	9.629%	$64.0562	$64.06	$64.05	$64.10
Purchase #3	$195.33	13.665%	$222.0218	$222.02	$222.00	$222.00
Purchase #4	$44.35	13.464%	$50.3213	$50.32	$50.30	$50.30
Purchase #5	$79.63	8.613%	$86.4885	$86.49	$86.50	$86.50
Purchase #6	$218.40	13.742%	$248.4125	$248.41	$248.40	$248.40
Purchase #7	$100.47	8.784%	$109.2953	$109.30	$109.30	$109.30
7 purchase totals =	$900.56		$998.0695	$998.07	$998.00	$998.10