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	$87.41	3.205%	$90.2115	$90.21	$90.20	$90.20
Purchase #2	$89.93	11.353%	$100.1398	$100.14	$100.15	$100.10
Purchase #3	$24.51	11.174%	$27.2487	$27.25	$27.25	$27.20
Purchase #4	$240.71	9.652%	$263.9433	$263.94	$263.95	$263.90
Purchase #5	$91.82	8.665%	$99.7762	$99.78	$99.80	$99.80
Purchase #6	$166.97	13.654%	$189.7681	$189.77	$189.75	$189.80
Purchase #7	$109.99	11.459%	$122.5938	$122.59	$122.60	$122.60
7 purchase totals =	$811.34		$893.6814	$893.68	$893.70	$893.60