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	$5.78	13.660%	$6.5695	$6.57	$6.55	$6.60
Purchase #2	$200.97	5.633%	$212.2906	$212.29	$212.30	$212.30
Purchase #3	$46.74	13.122%	$52.8732	$52.87	$52.85	$52.90
Purchase #4	$150.37	8.347%	$162.9214	$162.92	$162.90	$162.90
Purchase #5	$56.39	5.773%	$59.6454	$59.65	$59.65	$59.60
Purchase #6	$200.55	7.762%	$216.1167	$216.12	$216.10	$216.10
Purchase #7	$38.86	3.340%	$40.1579	$40.16	$40.15	$40.20
7 purchase totals =	$699.66		$750.5747	$750.58	$750.50	$750.60