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	$129.31	9.280%	$141.31	$141.31	$141.30	$141.30
Purchase #2	$156.67	4.783%	$164.1635	$164.16	$164.15	$164.20
Purchase #3	$48.44	9.755%	$53.1653	$53.17	$53.15	$53.20
Purchase #4	$166.51	8.321%	$180.3653	$180.37	$180.35	$180.40
Purchase #5	$152.48	4.229%	$158.9284	$158.93	$158.95	$158.90
Purchase #6	$34.60	11.572%	$38.6039	$38.60	$38.60	$38.60
Purchase #7	$96.30	9.339%	$105.2935	$105.29	$105.30	$105.30
7 purchase totals =	$784.31		$841.8299	$841.83	$841.80	$841.90