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	$77.73	4.819%	$81.4758	$81.48	$81.50	$81.50
Purchase #2	$46.67	12.242%	$52.3833	$52.38	$52.40	$52.40
Purchase #3	$36.50	5.707%	$38.5831	$38.58	$38.60	$38.60
Purchase #4	$90.32	13.666%	$102.6631	$102.66	$102.65	$102.70
Purchase #5	$75.39	13.485%	$85.5563	$85.56	$85.55	$85.60
Purchase #6	$150.67	9.372%	$164.7908	$164.79	$164.80	$164.80
Purchase #7	$44.39	8.653%	$48.2311	$48.23	$48.25	$48.20
7 purchase totals =	$521.67		$573.6835	$573.68	$573.75	$573.80