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	$26.71	9.852%	$29.3415	$29.34	$29.35	$29.30
Purchase #2	$54.35	9.141%	$59.3181	$59.32	$59.30	$59.30
Purchase #3	$103.46	6.665%	$110.3556	$110.36	$110.35	$110.40
Purchase #4	$9.35	5.799%	$9.8922	$9.89	$9.90	$9.90
Purchase #5	$54.66	3.326%	$56.478	$56.48	$56.50	$56.50
Purchase #6	$172.89	4.601%	$180.8447	$180.84	$180.85	$180.80
Purchase #7	$82.82	4.364%	$86.4343	$86.43	$86.45	$86.40
7 purchase totals =	$504.24		$532.6644	$532.66	$532.70	$532.60