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	$93.50	12.777%	$105.4465	$105.45	$105.45	$105.40
Purchase #2	$118.87	10.577%	$131.4429	$131.44	$131.45	$131.40
Purchase #3	$22.91	11.706%	$25.5918	$25.59	$25.60	$25.60
Purchase #4	$87.75	13.110%	$99.254	$99.25	$99.25	$99.30
Purchase #5	$127.44	3.241%	$131.5703	$131.57	$131.55	$131.60
Purchase #6	$228.46	10.115%	$251.5687	$251.57	$251.55	$251.60
Purchase #7	$132.28	4.473%	$138.1969	$138.20	$138.20	$138.20
7 purchase totals =	$811.21		$883.0711	$883.07	$883.05	$883.10