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	$244.72	5.840%	$259.0116	$259.01	$259.00	$259.00
Purchase #2	$155.82	10.862%	$172.7452	$172.75	$172.75	$172.70
Purchase #3	$152.82	9.590%	$167.4754	$167.48	$167.50	$167.50
Purchase #4	$159.51	4.297%	$166.3641	$166.36	$166.35	$166.40
Purchase #5	$19.48	9.514%	$21.3333	$21.33	$21.35	$21.30
Purchase #6	$104.55	11.430%	$116.5001	$116.50	$116.50	$116.50
Purchase #7	$22.66	8.370%	$24.5566	$24.56	$24.55	$24.60
7 purchase totals =	$859.56		$927.9863	$927.99	$928.00	$928.00