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	$121.45	5.314%	$127.9039	$127.90	$127.90	$127.90
Purchase #2	$72.93	8.726%	$79.2939	$79.29	$79.30	$79.30
Purchase #3	$141.98	11.526%	$158.3446	$158.34	$158.35	$158.30
Purchase #4	$18.78	12.230%	$21.0768	$21.08	$21.10	$21.10
Purchase #5	$142.72	13.558%	$162.07	$162.07	$162.05	$162.10
Purchase #6	$191.86	9.640%	$210.3553	$210.36	$210.35	$210.40
Purchase #7	$126.70	3.382%	$130.985	$130.99	$131.00	$131.00
7 purchase totals =	$816.42		$890.0295	$890.03	$890.05	$890.10