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	$22.25	11.777%	$24.8704	$24.87	$24.85	$24.90
Purchase #2	$41.41	4.777%	$43.3882	$43.39	$43.40	$43.40
Purchase #3	$100.89	10.585%	$111.5692	$111.57	$111.55	$111.60
Purchase #4	$39.69	7.114%	$42.5135	$42.51	$42.50	$42.50
Purchase #5	$83.69	9.444%	$91.5937	$91.59	$91.60	$91.60
Purchase #6	$217.90	7.626%	$234.5171	$234.52	$234.50	$234.50
Purchase #7	$136.37	12.306%	$153.1517	$153.15	$153.15	$153.20
7 purchase totals =	$642.20		$701.6038	$701.60	$701.55	$701.70