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	$108.64	5.321%	$114.4207	$114.42	$114.40	$114.40
Purchase #2	$128.80	7.606%	$138.5965	$138.60	$138.60	$138.60
Purchase #3	$191.72	12.574%	$215.8269	$215.83	$215.85	$215.80
Purchase #4	$146.98	8.803%	$159.9186	$159.92	$159.90	$159.90
Purchase #5	$110.33	6.106%	$117.0667	$117.07	$117.05	$117.10
Purchase #6	$192.76	11.735%	$215.3804	$215.38	$215.40	$215.40
Purchase #7	$119.41	9.123%	$130.3038	$130.30	$130.30	$130.30
7 purchase totals =	$998.64		$1,091.5136	$1,091.52	$1,091.50	$1,091.50