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	$152.64	12.382%	$171.5399	$171.54	$171.55	$171.50
Purchase #2	$30.51	12.407%	$34.2954	$34.30	$34.30	$34.30
Purchase #3	$55.73	6.771%	$59.5035	$59.50	$59.50	$59.50
Purchase #4	$141.89	13.516%	$161.0679	$161.07	$161.05	$161.10
Purchase #5	$123.71	13.163%	$139.9939	$139.99	$140.00	$140.00
Purchase #6	$92.49	11.672%	$103.2854	$103.29	$103.30	$103.30
Purchase #7	$6.81	8.508%	$7.3894	$7.39	$7.40	$7.40
7 purchase totals =	$603.78		$677.0754	$677.08	$677.10	$677.10