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	$99.46	9.732%	$109.1394	$109.14	$109.15	$109.10
Purchase #2	$39.93	9.300%	$43.6435	$43.64	$43.65	$43.60
Purchase #3	$131.87	4.740%	$138.1206	$138.12	$138.10	$138.10
Purchase #4	$164.38	9.492%	$179.9829	$179.98	$180.00	$180.00
Purchase #5	$107.62	5.655%	$113.7059	$113.71	$113.70	$113.70
Purchase #6	$85.60	4.834%	$89.7379	$89.74	$89.75	$89.70
Purchase #7	$189.73	8.481%	$205.821	$205.82	$205.80	$205.80
7 purchase totals =	$818.59		$880.1512	$880.15	$880.15	$880.00