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	$233.83	13.693%	$265.8483	$265.85	$265.85	$265.80
Purchase #2	$161.40	4.187%	$168.1578	$168.16	$168.15	$168.20
Purchase #3	$62.82	4.605%	$65.7129	$65.71	$65.70	$65.70
Purchase #4	$178.57	11.759%	$199.568	$199.57	$199.55	$199.60
Purchase #5	$82.55	8.137%	$89.2671	$89.27	$89.25	$89.30
Purchase #6	$51.59	3.205%	$53.2435	$53.24	$53.25	$53.20
Purchase #7	$70.87	12.636%	$79.8251	$79.83	$79.85	$79.80
7 purchase totals =	$841.63		$921.6227	$921.63	$921.60	$921.60