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	$31.38	4.824%	$32.8938	$32.89	$32.90	$32.90
Purchase #2	$146.64	10.583%	$162.1589	$162.16	$162.15	$162.20
Purchase #3	$81.91	4.441%	$85.5476	$85.55	$85.55	$85.50
Purchase #4	$168.68	4.686%	$176.5843	$176.58	$176.60	$176.60
Purchase #5	$162.78	13.242%	$184.3353	$184.34	$184.35	$184.30
Purchase #6	$173.27	6.329%	$184.2363	$184.24	$184.25	$184.20
Purchase #7	$99.91	10.516%	$110.4165	$110.42	$110.40	$110.40
7 purchase totals =	$864.57		$936.1727	$936.18	$936.20	$936.10