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	$73.54	6.672%	$78.4466	$78.45	$78.45	$78.40
Purchase #2	$69.70	11.192%	$77.5008	$77.50	$77.50	$77.50
Purchase #3	$148.57	9.557%	$162.7688	$162.77	$162.75	$162.80
Purchase #4	$165.37	4.175%	$172.2742	$172.27	$172.25	$172.30
Purchase #5	$225.32	13.401%	$255.5151	$255.52	$255.50	$255.50
Purchase #6	$101.73	6.425%	$108.2662	$108.27	$108.25	$108.30
Purchase #7	$36.92	10.446%	$40.7767	$40.78	$40.80	$40.80
7 purchase totals =	$821.15		$895.5484	$895.56	$895.50	$895.60