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	$11.60	5.613%	$12.2511	$12.25	$12.25	$12.30
Purchase #2	$179.63	7.502%	$193.1058	$193.11	$193.10	$193.10
Purchase #3	$124.59	13.747%	$141.7174	$141.72	$141.70	$141.70
Purchase #4	$28.33	12.737%	$31.9384	$31.94	$31.95	$31.90
Purchase #5	$173.74	12.814%	$196.003	$196.00	$196.00	$196.00
Purchase #6	$103.35	6.190%	$109.7474	$109.75	$109.75	$109.70
Purchase #7	$217.35	6.189%	$230.8018	$230.80	$230.80	$230.80
7 purchase totals =	$838.59		$915.5649	$915.57	$915.55	$915.50