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	$85.65	5.704%	$90.5355	$90.54	$90.55	$90.50
Purchase #2	$214.69	3.573%	$222.3609	$222.36	$222.35	$222.40
Purchase #3	$83.70	9.442%	$91.603	$91.60	$91.60	$91.60
Purchase #4	$166.86	8.839%	$181.6088	$181.61	$181.60	$181.60
Purchase #5	$34.84	12.754%	$39.2835	$39.28	$39.30	$39.30
Purchase #6	$31.82	4.400%	$33.2201	$33.22	$33.20	$33.20
Purchase #7	$160.61	8.558%	$174.355	$174.36	$174.35	$174.40
7 purchase totals =	$778.17		$832.9668	$832.97	$832.95	$833.00