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	$192.91	7.231%	$206.8593	$206.86	$206.85	$206.90
Purchase #2	$105.67	3.680%	$109.5587	$109.56	$109.55	$109.60
Purchase #3	$60.89	10.322%	$67.1751	$67.18	$67.20	$67.20
Purchase #4	$137.89	5.356%	$145.2754	$145.28	$145.30	$145.30
Purchase #5	$18.42	9.847%	$20.2338	$20.23	$20.25	$20.20
Purchase #6	$8.37	5.748%	$8.8511	$8.85	$8.85	$8.90
Purchase #7	$82.53	9.567%	$90.4256	$90.43	$90.45	$90.40
7 purchase totals =	$606.68		$648.3790	$648.39	$648.45	$648.50