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	$149.85	12.693%	$168.8705	$168.87	$168.85	$168.90
Purchase #2	$207.75	10.380%	$229.3145	$229.31	$229.30	$229.30
Purchase #3	$150.54	13.654%	$171.0947	$171.09	$171.10	$171.10
Purchase #4	$71.93	12.612%	$81.0018	$81.00	$81.00	$81.00
Purchase #5	$26.35	11.809%	$29.4617	$29.46	$29.45	$29.50
Purchase #6	$152.26	4.195%	$158.6473	$158.65	$158.65	$158.60
Purchase #7	$144.61	8.221%	$156.4984	$156.50	$156.50	$156.50
7 purchase totals =	$903.29		$994.8889	$994.88	$994.85	$994.90