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	$80.33	10.323%	$88.6225	$88.62	$88.60	$88.60
Purchase #2	$105.52	8.165%	$114.1357	$114.14	$114.15	$114.10
Purchase #3	$92.34	10.310%	$101.8603	$101.86	$101.85	$101.90
Purchase #4	$118.26	11.265%	$131.582	$131.58	$131.60	$131.60
Purchase #5	$206.88	3.274%	$213.6533	$213.65	$213.65	$213.70
Purchase #6	$159.32	13.328%	$180.5542	$180.55	$180.55	$180.60
Purchase #7	$233.62	3.176%	$241.0398	$241.04	$241.05	$241.00
7 purchase totals =	$996.27		$1,071.4478	$1,071.44	$1,071.45	$1,071.50