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	$121.98	7.711%	$131.3859	$131.39	$131.40	$131.40
Purchase #2	$22.26	8.187%	$24.0824	$24.08	$24.10	$24.10
Purchase #3	$131.37	13.762%	$149.4491	$149.45	$149.45	$149.40
Purchase #4	$247.46	11.262%	$275.3289	$275.33	$275.35	$275.30
Purchase #5	$31.93	5.291%	$33.6194	$33.62	$33.60	$33.60
Purchase #6	$179.85	6.491%	$191.5241	$191.52	$191.50	$191.50
Purchase #7	$81.37	9.617%	$89.1954	$89.20	$89.20	$89.20
7 purchase totals =	$816.22		$894.5852	$894.59	$894.60	$894.50