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	$210.29	8.651%	$228.4822	$228.48	$228.50	$228.50
Purchase #2	$70.76	12.859%	$79.859	$79.86	$79.85	$79.90
Purchase #3	$82.72	12.653%	$93.1866	$93.19	$93.20	$93.20
Purchase #4	$40.90	13.379%	$46.372	$46.37	$46.35	$46.40
Purchase #5	$42.80	10.453%	$47.2739	$47.27	$47.25	$47.30
Purchase #6	$106.52	11.278%	$118.5333	$118.53	$118.55	$118.50
Purchase #7	$92.95	6.602%	$99.0866	$99.09	$99.10	$99.10
7 purchase totals =	$646.94		$712.7936	$712.79	$712.80	$712.90