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	$83.30	7.202%	$89.2993	$89.30	$89.30	$89.30
Purchase #2	$170.87	5.137%	$179.6476	$179.65	$179.65	$179.60
Purchase #3	$125.34	12.828%	$141.4186	$141.42	$141.40	$141.40
Purchase #4	$17.80	10.304%	$19.6341	$19.63	$19.65	$19.60
Purchase #5	$147.52	7.217%	$158.1665	$158.17	$158.15	$158.20
Purchase #6	$227.72	7.260%	$244.2525	$244.25	$244.25	$244.30
Purchase #7	$192.73	8.240%	$208.611	$208.61	$208.60	$208.60
7 purchase totals =	$965.28		$1,041.0296	$1,041.03	$1,041.00	$1,041.00