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	$58.94	13.600%	$66.9558	$66.96	$66.95	$67.00
Purchase #2	$117.32	3.594%	$121.5365	$121.54	$121.55	$121.50
Purchase #3	$81.38	8.693%	$88.4544	$88.45	$88.45	$88.50
Purchase #4	$72.73	10.686%	$80.5019	$80.50	$80.50	$80.50
Purchase #5	$153.62	13.568%	$174.4632	$174.46	$174.45	$174.50
Purchase #6	$79.75	13.196%	$90.2738	$90.27	$90.25	$90.30
Purchase #7	$176.88	13.129%	$200.1026	$200.10	$200.10	$200.10
7 purchase totals =	$740.62		$822.2882	$822.28	$822.25	$822.40