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	$171.28	5.802%	$181.2177	$181.22	$181.20	$181.20
Purchase #2	$127.76	3.678%	$132.459	$132.46	$132.45	$132.50
Purchase #3	$116.44	12.636%	$131.1534	$131.15	$131.15	$131.20
Purchase #4	$93.33	12.115%	$104.6369	$104.64	$104.65	$104.60
Purchase #5	$90.89	7.874%	$98.0467	$98.05	$98.05	$98.00
Purchase #6	$91.80	9.662%	$100.6697	$100.67	$100.65	$100.70
Purchase #7	$129.87	9.698%	$142.4648	$142.46	$142.45	$142.50
7 purchase totals =	$821.37		$890.6482	$890.65	$890.60	$890.70