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	$117.71	5.196%	$123.8262	$123.83	$123.85	$123.80
Purchase #2	$234.38	7.564%	$252.1085	$252.11	$252.10	$252.10
Purchase #3	$118.50	5.538%	$125.0625	$125.06	$125.05	$125.10
Purchase #4	$148.57	10.610%	$164.3333	$164.33	$164.35	$164.30
Purchase #5	$218.56	5.381%	$230.3207	$230.32	$230.30	$230.30
Purchase #6	$42.96	4.780%	$45.0135	$45.01	$45.00	$45.00
Purchase #7	$38.78	6.420%	$41.2697	$41.27	$41.25	$41.30
7 purchase totals =	$919.46		$981.9344	$981.93	$981.90	$981.90