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	$93.42	3.539%	$96.7261	$96.73	$96.75	$96.70
Purchase #2	$156.50	10.224%	$172.5006	$172.50	$172.50	$172.50
Purchase #3	$53.94	6.543%	$57.4693	$57.47	$57.45	$57.50
Purchase #4	$21.48	13.629%	$24.4075	$24.41	$24.40	$24.40
Purchase #5	$52.37	5.672%	$55.3404	$55.34	$55.35	$55.30
Purchase #6	$123.60	6.265%	$131.3435	$131.34	$131.35	$131.30
Purchase #7	$248.98	12.328%	$279.6743	$279.67	$279.65	$279.70
7 purchase totals =	$750.29		$817.4617	$817.46	$817.45	$817.40