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	$137.33	7.649%	$147.8344	$147.83	$147.85	$147.80
Purchase #2	$113.74	13.670%	$129.2883	$129.29	$129.30	$129.30
Purchase #3	$245.41	6.807%	$262.1151	$262.12	$262.10	$262.10
Purchase #4	$90.56	8.665%	$98.407	$98.41	$98.40	$98.40
Purchase #5	$83.28	8.749%	$90.5662	$90.57	$90.55	$90.60
Purchase #6	$66.64	3.208%	$68.7778	$68.78	$68.80	$68.80
Purchase #7	$139.27	4.528%	$145.5761	$145.58	$145.60	$145.60
7 purchase totals =	$876.23		$942.5649	$942.58	$942.60	$942.60