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	$20.87	5.693%	$22.0581	$22.06	$22.05	$22.10
Purchase #2	$53.57	10.287%	$59.0807	$59.08	$59.10	$59.10
Purchase #3	$75.36	9.212%	$82.3022	$82.30	$82.30	$82.30
Purchase #4	$166.79	4.706%	$174.6391	$174.64	$174.65	$174.60
Purchase #5	$34.25	8.645%	$37.2109	$37.21	$37.20	$37.20
Purchase #6	$63.59	13.291%	$72.0417	$72.04	$72.05	$72.00
Purchase #7	$196.99	10.793%	$218.2511	$218.25	$218.25	$218.30
7 purchase totals =	$611.42		$665.5838	$665.58	$665.60	$665.60