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	$62.44	7.637%	$67.2085	$67.21	$67.20	$67.20
Purchase #2	$18.51	9.319%	$20.2349	$20.23	$20.25	$20.20
Purchase #3	$6.67	10.233%	$7.3525	$7.35	$7.35	$7.40
Purchase #4	$87.47	5.461%	$92.2467	$92.25	$92.25	$92.20
Purchase #5	$114.89	4.551%	$120.1186	$120.12	$120.10	$120.10
Purchase #6	$131.72	6.226%	$139.9209	$139.92	$139.90	$139.90
Purchase #7	$29.50	6.146%	$31.3131	$31.31	$31.30	$31.30
7 purchase totals =	$451.20		$478.3952	$478.39	$478.35	$478.30