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	$84.97	5.719%	$89.8294	$89.83	$89.85	$89.80
Purchase #2	$194.72	7.766%	$209.842	$209.84	$209.85	$209.80
Purchase #3	$167.29	8.311%	$181.1935	$181.19	$181.20	$181.20
Purchase #4	$111.80	3.572%	$115.7935	$115.79	$115.80	$115.80
Purchase #5	$58.89	5.353%	$62.0424	$62.04	$62.05	$62.00
Purchase #6	$44.81	10.190%	$49.3761	$49.38	$49.40	$49.40
Purchase #7	$57.40	3.843%	$59.6059	$59.61	$59.60	$59.60
7 purchase totals =	$719.88		$767.6828	$767.68	$767.75	$767.60