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	$147.76	12.761%	$166.6157	$166.62	$166.60	$166.60
Purchase #2	$143.69	5.624%	$151.7711	$151.77	$151.75	$151.80
Purchase #3	$169.46	11.198%	$188.4361	$188.44	$188.45	$188.40
Purchase #4	$170.62	9.434%	$186.7163	$186.72	$186.70	$186.70
Purchase #5	$249.79	13.797%	$284.2535	$284.25	$284.25	$284.30
Purchase #6	$170.81	5.825%	$180.7597	$180.76	$180.75	$180.80
Purchase #7	$90.35	7.268%	$96.9166	$96.92	$96.90	$96.90
7 purchase totals =	$1,142.48		$1,255.4690	$1,255.48	$1,255.40	$1,255.50