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	$172.52	9.482%	$188.8783	$188.88	$188.90	$188.90
Purchase #2	$141.45	6.116%	$150.1011	$150.10	$150.10	$150.10
Purchase #3	$211.56	6.743%	$225.8255	$225.83	$225.85	$225.80
Purchase #4	$14.89	10.413%	$16.4405	$16.44	$16.45	$16.40
Purchase #5	$60.38	10.248%	$66.5677	$66.57	$66.55	$66.60
Purchase #6	$142.54	5.294%	$150.0861	$150.09	$150.10	$150.10
Purchase #7	$160.56	13.322%	$181.9498	$181.95	$181.95	$181.90
7 purchase totals =	$903.90		$979.8490	$979.86	$979.90	$979.80