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	$143.89	3.232%	$148.5405	$148.54	$148.55	$148.50
Purchase #2	$75.79	6.761%	$80.9142	$80.91	$80.90	$80.90
Purchase #3	$105.54	7.320%	$113.2655	$113.27	$113.25	$113.30
Purchase #4	$128.68	11.483%	$143.4563	$143.46	$143.45	$143.50
Purchase #5	$64.50	7.117%	$69.0905	$69.09	$69.10	$69.10
Purchase #6	$130.73	7.533%	$140.5779	$140.58	$140.60	$140.60
Purchase #7	$215.27	3.310%	$222.3954	$222.40	$222.40	$222.40
7 purchase totals =	$864.40		$918.2403	$918.25	$918.25	$918.30