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	$66.96	8.227%	$72.4688	$72.47	$72.45	$72.50
Purchase #2	$116.51	3.803%	$120.9409	$120.94	$120.95	$120.90
Purchase #3	$18.50	9.210%	$20.2039	$20.20	$20.20	$20.20
Purchase #4	$166.84	13.524%	$189.4034	$189.40	$189.40	$189.40
Purchase #5	$176.74	11.159%	$196.4624	$196.46	$196.45	$196.50
Purchase #6	$113.39	12.313%	$127.3517	$127.35	$127.35	$127.40
Purchase #7	$10.58	13.245%	$11.9813	$11.98	$12.00	$12.00
7 purchase totals =	$669.52		$738.8124	$738.80	$738.80	$738.90