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	$120.42	4.150%	$125.4174	$125.42	$125.40	$125.40
Purchase #2	$132.74	8.757%	$144.364	$144.36	$144.35	$144.40
Purchase #3	$67.53	13.351%	$76.5459	$76.55	$76.55	$76.50
Purchase #4	$67.40	7.385%	$72.3775	$72.38	$72.40	$72.40
Purchase #5	$76.58	7.388%	$82.2377	$82.24	$82.25	$82.20
Purchase #6	$53.79	13.581%	$61.0952	$61.10	$61.10	$61.10
Purchase #7	$70.29	9.860%	$77.2206	$77.22	$77.20	$77.20
7 purchase totals =	$588.75		$639.2583	$639.27	$639.25	$639.20