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	$40.56	5.469%	$42.7782	$42.78	$42.80	$42.80
Purchase #2	$91.87	11.345%	$102.2927	$102.29	$102.30	$102.30
Purchase #3	$61.40	6.307%	$65.2725	$65.27	$65.25	$65.30
Purchase #4	$79.58	3.808%	$82.6104	$82.61	$82.60	$82.60
Purchase #5	$167.72	9.572%	$183.7742	$183.77	$183.75	$183.80
Purchase #6	$99.81	12.551%	$112.3372	$112.34	$112.35	$112.30
Purchase #7	$122.65	10.210%	$135.1726	$135.17	$135.15	$135.20
7 purchase totals =	$663.59		$724.2378	$724.23	$724.20	$724.30