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	$233.87	13.639%	$265.7675	$265.77	$265.75	$265.80
Purchase #2	$74.94	13.104%	$84.7601	$84.76	$84.75	$84.80
Purchase #3	$75.89	13.120%	$85.8468	$85.85	$85.85	$85.80
Purchase #4	$87.35	3.717%	$90.5968	$90.60	$90.60	$90.60
Purchase #5	$81.41	5.128%	$85.5847	$85.58	$85.60	$85.60
Purchase #6	$70.35	13.832%	$80.0808	$80.08	$80.10	$80.10
Purchase #7	$45.27	3.580%	$46.8907	$46.89	$46.90	$46.90
7 purchase totals =	$669.08		$739.5274	$739.53	$739.55	$739.60