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	$17.70	4.172%	$18.4384	$18.44	$18.45	$18.40
Purchase #2	$73.78	10.356%	$81.4207	$81.42	$81.40	$81.40
Purchase #3	$132.52	13.833%	$150.8515	$150.85	$150.85	$150.90
Purchase #4	$62.51	10.546%	$69.1023	$69.10	$69.10	$69.10
Purchase #5	$103.94	6.237%	$110.4227	$110.42	$110.40	$110.40
Purchase #6	$84.88	6.707%	$90.5729	$90.57	$90.55	$90.60
Purchase #7	$50.68	6.133%	$53.7882	$53.79	$53.80	$53.80
7 purchase totals =	$526.01		$574.5967	$574.59	$574.55	$574.60