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	$18.26	10.778%	$20.2281	$20.23	$20.25	$20.20
Purchase #2	$127.92	13.787%	$145.5563	$145.56	$145.55	$145.60
Purchase #3	$164.67	9.192%	$179.8065	$179.81	$179.80	$179.80
Purchase #4	$71.50	6.327%	$76.0238	$76.02	$76.00	$76.00
Purchase #5	$154.51	4.159%	$160.9361	$160.94	$160.95	$160.90
Purchase #6	$122.83	3.460%	$127.0799	$127.08	$127.10	$127.10
Purchase #7	$48.41	4.265%	$50.4747	$50.47	$50.45	$50.50
7 purchase totals =	$708.10		$760.1054	$760.11	$760.10	$760.10