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	$95.86	7.590%	$103.1358	$103.14	$103.15	$103.10
Purchase #2	$113.82	5.615%	$120.211	$120.21	$120.20	$120.20
Purchase #3	$136.49	12.584%	$153.6659	$153.67	$153.65	$153.70
Purchase #4	$67.80	7.473%	$72.8667	$72.87	$72.85	$72.90
Purchase #5	$86.30	3.493%	$89.3145	$89.31	$89.30	$89.30
Purchase #6	$237.94	11.660%	$265.6838	$265.68	$265.70	$265.70
Purchase #7	$109.82	7.613%	$118.1806	$118.18	$118.20	$118.20
7 purchase totals =	$848.03		$923.0583	$923.06	$923.05	$923.10