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	$51.30	9.601%	$56.2253	$56.23	$56.25	$56.20
Purchase #2	$154.83	10.369%	$170.8843	$170.88	$170.90	$170.90
Purchase #3	$123.95	9.352%	$135.5418	$135.54	$135.55	$135.50
Purchase #4	$79.88	13.297%	$90.5016	$90.50	$90.50	$90.50
Purchase #5	$95.51	7.318%	$102.4994	$102.50	$102.50	$102.50
Purchase #6	$240.28	4.109%	$250.1531	$250.15	$250.15	$250.20
Purchase #7	$29.68	13.437%	$33.6681	$33.67	$33.65	$33.70
7 purchase totals =	$775.43		$839.4736	$839.47	$839.50	$839.50