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	$21.49	12.689%	$24.2169	$24.22	$24.20	$24.20
Purchase #2	$195.51	13.436%	$221.7787	$221.78	$221.80	$221.80
Purchase #3	$52.54	12.535%	$59.1259	$59.13	$59.15	$59.10
Purchase #4	$56.58	5.580%	$59.7372	$59.74	$59.75	$59.70
Purchase #5	$11.79	4.593%	$12.3315	$12.33	$12.35	$12.30
Purchase #6	$77.99	5.316%	$82.1359	$82.14	$82.15	$82.10
Purchase #7	$8.40	5.111%	$8.8293	$8.83	$8.85	$8.80
7 purchase totals =	$424.30		$468.1554	$468.17	$468.25	$468.00