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	$83.95	6.188%	$89.1448	$89.14	$89.15	$89.10
Purchase #2	$150.55	10.207%	$165.9166	$165.92	$165.90	$165.90
Purchase #3	$214.80	3.270%	$221.824	$221.82	$221.80	$221.80
Purchase #4	$140.45	9.697%	$154.0694	$154.07	$154.05	$154.10
Purchase #5	$48.59	4.574%	$50.8125	$50.81	$50.80	$50.80
Purchase #6	$151.91	8.372%	$164.6279	$164.63	$164.65	$164.60
Purchase #7	$89.55	5.157%	$94.1681	$94.17	$94.15	$94.20
7 purchase totals =	$879.80		$940.5633	$940.56	$940.50	$940.50