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	$19.36	10.813%	$21.4534	$21.45	$21.45	$21.50
Purchase #2	$68.45	3.421%	$70.7917	$70.79	$70.80	$70.80
Purchase #3	$112.78	9.654%	$123.6678	$123.67	$123.65	$123.70
Purchase #4	$82.94	5.216%	$87.2662	$87.27	$87.25	$87.30
Purchase #5	$226.60	10.819%	$251.1159	$251.12	$251.10	$251.10
Purchase #6	$68.94	3.384%	$71.2729	$71.27	$71.25	$71.30
Purchase #7	$89.52	3.276%	$92.4527	$92.45	$92.45	$92.50
7 purchase totals =	$668.59		$718.0206	$718.02	$717.95	$718.20