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	$29.45	13.251%	$33.3524	$33.35	$33.35	$33.40
Purchase #2	$164.85	5.397%	$173.747	$173.75	$173.75	$173.70
Purchase #3	$126.54	10.837%	$140.2531	$140.25	$140.25	$140.30
Purchase #4	$107.46	3.432%	$111.148	$111.15	$111.15	$111.10
Purchase #5	$39.40	11.279%	$43.8439	$43.84	$43.85	$43.80
Purchase #6	$53.79	5.385%	$56.6866	$56.69	$56.70	$56.70
Purchase #7	$68.52	13.505%	$77.7736	$77.77	$77.75	$77.80
7 purchase totals =	$590.01		$636.8046	$636.80	$636.80	$636.80