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	$108.49	13.395%	$123.0222	$123.02	$123.00	$123.00
Purchase #2	$238.65	4.386%	$249.1172	$249.12	$249.10	$249.10
Purchase #3	$164.55	11.451%	$183.3926	$183.39	$183.40	$183.40
Purchase #4	$29.49	6.209%	$31.321	$31.32	$31.30	$31.30
Purchase #5	$104.72	8.194%	$113.3008	$113.30	$113.30	$113.30
Purchase #6	$82.55	10.232%	$90.9965	$91.00	$91.00	$91.00
Purchase #7	$51.61	7.303%	$55.3791	$55.38	$55.40	$55.40
7 purchase totals =	$780.06		$846.5294	$846.53	$846.50	$846.50