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	$160.63	12.399%	$180.5465	$180.55	$180.55	$180.50
Purchase #2	$78.55	10.608%	$86.8826	$86.88	$86.90	$86.90
Purchase #3	$69.56	10.496%	$76.861	$76.86	$76.85	$76.90
Purchase #4	$60.82	9.832%	$66.7998	$66.80	$66.80	$66.80
Purchase #5	$68.49	11.546%	$76.3979	$76.40	$76.40	$76.40
Purchase #6	$77.95	10.229%	$85.9235	$85.92	$85.90	$85.90
Purchase #7	$129.25	6.136%	$137.1808	$137.18	$137.20	$137.20
7 purchase totals =	$645.25		$710.5921	$710.59	$710.60	$710.60