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	$250.38	11.246%	$278.5377	$278.54	$278.55	$278.50
Purchase #2	$12.59	10.280%	$13.8843	$13.88	$13.90	$13.90
Purchase #3	$141.41	7.650%	$152.2279	$152.23	$152.25	$152.20
Purchase #4	$93.39	6.268%	$99.2437	$99.24	$99.25	$99.20
Purchase #5	$36.84	8.830%	$40.093	$40.09	$40.10	$40.10
Purchase #6	$103.45	5.562%	$109.2039	$109.20	$109.20	$109.20
Purchase #7	$20.82	9.431%	$22.7835	$22.78	$22.80	$22.80
7 purchase totals =	$658.88		$715.9740	$715.96	$716.05	$715.90