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	$66.53	5.203%	$69.9916	$69.99	$70.00	$70.00
Purchase #2	$93.82	10.219%	$103.4075	$103.41	$103.40	$103.40
Purchase #3	$36.77	13.230%	$41.6347	$41.63	$41.65	$41.60
Purchase #4	$101.40	4.461%	$105.9235	$105.92	$105.90	$105.90
Purchase #5	$57.77	6.567%	$61.5638	$61.56	$61.55	$61.60
Purchase #6	$46.47	8.728%	$50.5259	$50.53	$50.55	$50.50
Purchase #7	$159.40	12.382%	$179.1369	$179.14	$179.15	$179.10
7 purchase totals =	$562.16		$612.1839	$612.18	$612.20	$612.10