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	$200.61	10.141%	$220.9539	$220.95	$220.95	$221.00
Purchase #2	$249.45	4.679%	$261.1218	$261.12	$261.10	$261.10
Purchase #3	$93.83	7.131%	$100.521	$100.52	$100.50	$100.50
Purchase #4	$167.58	12.222%	$188.0616	$188.06	$188.05	$188.10
Purchase #5	$199.33	10.152%	$219.566	$219.57	$219.55	$219.60
Purchase #6	$226.33	3.376%	$233.9709	$233.97	$233.95	$234.00
Purchase #7	$85.25	13.610%	$96.8525	$96.85	$96.85	$96.90
7 purchase totals =	$1,222.38		$1,321.0477	$1,321.04	$1,320.95	$1,321.20