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	$106.88	7.193%	$114.5679	$114.57	$114.55	$114.60
Purchase #2	$105.83	12.731%	$119.3032	$119.30	$119.30	$119.30
Purchase #3	$59.29	13.814%	$67.4803	$67.48	$67.50	$67.50
Purchase #4	$150.65	5.493%	$158.9252	$158.93	$158.95	$158.90
Purchase #5	$14.28	4.415%	$14.9105	$14.91	$14.90	$14.90
Purchase #6	$58.25	12.445%	$65.4992	$65.50	$65.50	$65.50
Purchase #7	$130.57	6.785%	$139.4292	$139.43	$139.45	$139.40
7 purchase totals =	$625.75		$680.1155	$680.12	$680.15	$680.10