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	$55.44	10.598%	$61.3155	$61.32	$61.30	$61.30
Purchase #2	$147.70	11.331%	$164.4359	$164.44	$164.45	$164.40
Purchase #3	$80.67	11.576%	$90.0084	$90.01	$90.00	$90.00
Purchase #4	$161.88	10.654%	$179.1267	$179.13	$179.15	$179.10
Purchase #5	$41.51	5.831%	$43.9304	$43.93	$43.95	$43.90
Purchase #6	$28.72	11.788%	$32.1055	$32.11	$32.10	$32.10
Purchase #7	$179.91	13.624%	$204.4209	$204.42	$204.40	$204.40
7 purchase totals =	$695.83		$775.3433	$775.36	$775.35	$775.20