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	$51.99	8.842%	$56.587	$56.59	$56.60	$56.60
Purchase #2	$236.53	10.539%	$261.4579	$261.46	$261.45	$261.50
Purchase #3	$207.89	13.335%	$235.6121	$235.61	$235.60	$235.60
Purchase #4	$78.84	8.810%	$85.7858	$85.79	$85.80	$85.80
Purchase #5	$18.42	9.412%	$20.1537	$20.15	$20.15	$20.20
Purchase #6	$137.75	6.290%	$146.4145	$146.41	$146.40	$146.40
Purchase #7	$93.91	9.824%	$103.1357	$103.14	$103.15	$103.10
7 purchase totals =	$825.33		$909.1467	$909.15	$909.15	$909.20