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	$76.31	7.300%	$81.8806	$81.88	$81.90	$81.90
Purchase #2	$37.27	3.457%	$38.5584	$38.56	$38.55	$38.60
Purchase #3	$41.61	13.462%	$47.2115	$47.21	$47.20	$47.20
Purchase #4	$225.67	10.851%	$250.1575	$250.16	$250.15	$250.20
Purchase #5	$25.82	9.410%	$28.2497	$28.25	$28.25	$28.20
Purchase #6	$10.58	13.308%	$11.988	$11.99	$12.00	$12.00
Purchase #7	$119.64	3.135%	$123.3907	$123.39	$123.40	$123.40
7 purchase totals =	$536.90		$581.4364	$581.44	$581.45	$581.50