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	$127.56	9.340%	$139.4741	$139.47	$139.45	$139.50
Purchase #2	$41.80	13.822%	$47.5776	$47.58	$47.60	$47.60
Purchase #3	$78.90	8.658%	$85.7312	$85.73	$85.75	$85.70
Purchase #4	$220.42	5.344%	$232.1992	$232.20	$232.20	$232.20
Purchase #5	$200.38	7.649%	$215.7071	$215.71	$215.70	$215.70
Purchase #6	$98.92	12.783%	$111.5649	$111.56	$111.55	$111.60
Purchase #7	$75.33	3.678%	$78.1006	$78.10	$78.10	$78.10
7 purchase totals =	$843.31		$910.3547	$910.35	$910.35	$910.40