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	$244.59	9.260%	$267.239	$267.24	$267.25	$267.20
Purchase #2	$104.69	13.315%	$118.6295	$118.63	$118.65	$118.60
Purchase #3	$79.51	3.773%	$82.5099	$82.51	$82.50	$82.50
Purchase #4	$192.42	4.407%	$200.8999	$200.90	$200.90	$200.90
Purchase #5	$84.89	6.279%	$90.2202	$90.22	$90.20	$90.20
Purchase #6	$41.68	6.632%	$44.4442	$44.44	$44.45	$44.40
Purchase #7	$93.65	3.394%	$96.8285	$96.83	$96.85	$96.80
7 purchase totals =	$841.43		$900.7712	$900.77	$900.80	$900.60