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	$150.69	8.866%	$164.0502	$164.05	$164.05	$164.10
Purchase #2	$41.72	10.612%	$46.1473	$46.15	$46.15	$46.10
Purchase #3	$59.42	10.165%	$65.46	$65.46	$65.45	$65.50
Purchase #4	$72.86	13.254%	$82.5169	$82.52	$82.50	$82.50
Purchase #5	$130.43	12.275%	$146.4403	$146.44	$146.45	$146.40
Purchase #6	$168.63	12.332%	$189.4255	$189.43	$189.45	$189.40
Purchase #7	$103.82	11.491%	$115.75	$115.75	$115.75	$115.80
7 purchase totals =	$727.57		$809.7902	$809.80	$809.80	$809.80