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	$18.70	5.403%	$19.7104	$19.71	$19.70	$19.70
Purchase #2	$45.76	4.862%	$47.9849	$47.98	$48.00	$48.00
Purchase #3	$154.51	13.129%	$174.7956	$174.80	$174.80	$174.80
Purchase #4	$33.50	12.275%	$37.6121	$37.61	$37.60	$37.60
Purchase #5	$101.93	11.767%	$113.9241	$113.92	$113.90	$113.90
Purchase #6	$132.66	3.668%	$137.526	$137.53	$137.55	$137.50
Purchase #7	$147.41	3.673%	$152.8244	$152.82	$152.80	$152.80
7 purchase totals =	$634.47		$684.3775	$684.37	$684.35	$684.30