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	$206.77	6.694%	$220.6112	$220.61	$220.60	$220.60
Purchase #2	$36.80	12.278%	$41.3183	$41.32	$41.30	$41.30
Purchase #3	$57.68	6.408%	$61.3761	$61.38	$61.40	$61.40
Purchase #4	$66.41	3.300%	$68.6015	$68.60	$68.60	$68.60
Purchase #5	$104.83	6.427%	$111.5674	$111.57	$111.55	$111.60
Purchase #6	$82.25	8.761%	$89.4559	$89.46	$89.45	$89.50
Purchase #7	$37.58	4.305%	$39.1978	$39.20	$39.20	$39.20
7 purchase totals =	$592.32		$632.1282	$632.14	$632.10	$632.20