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	$192.32	3.752%	$199.5358	$199.54	$199.55	$199.50
Purchase #2	$87.98	6.700%	$93.8747	$93.87	$93.85	$93.90
Purchase #3	$80.70	11.866%	$90.2759	$90.28	$90.30	$90.30
Purchase #4	$30.37	13.735%	$34.5413	$34.54	$34.55	$34.50
Purchase #5	$104.44	13.718%	$118.7671	$118.77	$118.75	$118.80
Purchase #6	$39.63	13.423%	$44.9495	$44.95	$44.95	$44.90
Purchase #7	$86.43	4.669%	$90.4654	$90.47	$90.45	$90.50
7 purchase totals =	$621.87		$672.4097	$672.42	$672.40	$672.40