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	$99.71	9.454%	$109.1366	$109.14	$109.15	$109.10
Purchase #2	$53.58	10.348%	$59.1245	$59.12	$59.10	$59.10
Purchase #3	$194.39	7.680%	$209.3192	$209.32	$209.30	$209.30
Purchase #4	$25.71	6.385%	$27.3516	$27.35	$27.35	$27.40
Purchase #5	$214.72	8.673%	$233.3427	$233.34	$233.35	$233.30
Purchase #6	$109.80	10.684%	$121.531	$121.53	$121.55	$121.50
Purchase #7	$70.49	12.394%	$79.2265	$79.23	$79.25	$79.20
7 purchase totals =	$768.40		$839.0321	$839.03	$839.05	$838.90