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	$70.68	13.732%	$80.3858	$80.39	$80.40	$80.40
Purchase #2	$95.96	8.501%	$104.1176	$104.12	$104.10	$104.10
Purchase #3	$144.92	12.359%	$162.8307	$162.83	$162.85	$162.80
Purchase #4	$18.47	6.807%	$19.7273	$19.73	$19.75	$19.70
Purchase #5	$56.29	5.617%	$59.4518	$59.45	$59.45	$59.50
Purchase #6	$91.54	6.204%	$97.2191	$97.22	$97.20	$97.20
Purchase #7	$34.73	7.510%	$37.3382	$37.34	$37.35	$37.30
7 purchase totals =	$512.59		$561.0705	$561.08	$561.10	$561.00