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	$135.68	12.151%	$152.1665	$152.17	$152.15	$152.20
Purchase #2	$108.90	7.816%	$117.4116	$117.41	$117.40	$117.40
Purchase #3	$59.65	3.418%	$61.6888	$61.69	$61.70	$61.70
Purchase #4	$8.78	10.161%	$9.6721	$9.67	$9.65	$9.70
Purchase #5	$53.75	10.736%	$59.5206	$59.52	$59.50	$59.50
Purchase #6	$103.41	5.537%	$109.1358	$109.14	$109.15	$109.10
Purchase #7	$45.86	6.480%	$48.8317	$48.83	$48.85	$48.80
7 purchase totals =	$516.03		$558.4271	$558.43	$558.40	$558.40