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	$5.83	4.706%	$6.1044	$6.10	$6.10	$6.10
Purchase #2	$89.98	3.199%	$92.8585	$92.86	$92.85	$92.90
Purchase #3	$217.42	9.475%	$238.0205	$238.02	$238.00	$238.00
Purchase #4	$199.67	8.585%	$216.8117	$216.81	$216.80	$216.80
Purchase #5	$181.35	5.122%	$190.6387	$190.64	$190.65	$190.60
Purchase #6	$102.59	6.623%	$109.3845	$109.38	$109.40	$109.40
Purchase #7	$225.83	3.254%	$233.1785	$233.18	$233.20	$233.20
7 purchase totals =	$1,022.67		$1,086.9968	$1,086.99	$1,087.00	$1,087.00