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	$93.38	10.637%	$103.3128	$103.31	$103.30	$103.30
Purchase #2	$124.99	5.872%	$132.3294	$132.33	$132.35	$132.30
Purchase #3	$90.78	9.138%	$99.0755	$99.08	$99.10	$99.10
Purchase #4	$20.66	5.111%	$21.7159	$21.72	$21.70	$21.70
Purchase #5	$146.62	8.296%	$158.7836	$158.78	$158.80	$158.80
Purchase #6	$154.86	5.222%	$162.9468	$162.95	$162.95	$162.90
Purchase #7	$25.93	7.734%	$27.9354	$27.94	$27.95	$27.90
7 purchase totals =	$657.22		$706.0994	$706.11	$706.15	$706.00