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	$108.55	13.424%	$123.1218	$123.12	$123.10	$123.10
Purchase #2	$240.38	6.477%	$255.9494	$255.95	$255.95	$255.90
Purchase #3	$59.48	11.278%	$66.1882	$66.19	$66.20	$66.20
Purchase #4	$118.91	4.763%	$124.5737	$124.57	$124.55	$124.60
Purchase #5	$166.75	5.700%	$176.2548	$176.25	$176.25	$176.30
Purchase #6	$5.64	6.852%	$6.0265	$6.03	$6.05	$6.00
Purchase #7	$123.98	11.250%	$137.9278	$137.93	$137.95	$137.90
7 purchase totals =	$823.69		$890.0422	$890.04	$890.05	$890.00