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	$5.68	9.429%	$6.2156	$6.22	$6.20	$6.20
Purchase #2	$244.72	7.570%	$263.2453	$263.25	$263.25	$263.20
Purchase #3	$17.63	10.571%	$19.4937	$19.49	$19.50	$19.50
Purchase #4	$172.61	9.196%	$188.4832	$188.48	$188.50	$188.50
Purchase #5	$42.40	3.143%	$43.7326	$43.73	$43.75	$43.70
Purchase #6	$187.72	5.719%	$198.4557	$198.46	$198.45	$198.50
Purchase #7	$146.27	9.143%	$159.6435	$159.64	$159.65	$159.60
7 purchase totals =	$817.03		$879.2696	$879.27	$879.30	$879.20