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	$227.94	13.507%	$258.7279	$258.73	$258.75	$258.70
Purchase #2	$166.29	8.161%	$179.8609	$179.86	$179.85	$179.90
Purchase #3	$190.40	8.161%	$205.9385	$205.94	$205.95	$205.90
Purchase #4	$148.28	12.501%	$166.8165	$166.82	$166.80	$166.80
Purchase #5	$6.86	4.390%	$7.1612	$7.16	$7.15	$7.20
Purchase #6	$163.97	9.367%	$179.3291	$179.33	$179.35	$179.30
Purchase #7	$14.42	3.858%	$14.9763	$14.98	$15.00	$15.00
7 purchase totals =	$918.16		$1,012.8104	$1,012.82	$1,012.85	$1,012.80