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	$55.71	6.409%	$59.2805	$59.28	$59.30	$59.30
Purchase #2	$62.98	5.569%	$66.4874	$66.49	$66.50	$66.50
Purchase #3	$43.57	13.587%	$49.4899	$49.49	$49.50	$49.50
Purchase #4	$48.67	12.461%	$54.7348	$54.73	$54.75	$54.70
Purchase #5	$186.33	9.375%	$203.7984	$203.80	$203.80	$203.80
Purchase #6	$46.97	8.286%	$50.8619	$50.86	$50.85	$50.90
Purchase #7	$141.42	7.849%	$152.5201	$152.52	$152.50	$152.50
7 purchase totals =	$585.65		$637.1730	$637.17	$637.20	$637.20