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	$121.83	4.151%	$126.8872	$126.89	$126.90	$126.90
Purchase #2	$92.33	13.758%	$105.0328	$105.03	$105.05	$105.00
Purchase #3	$133.86	13.605%	$152.0717	$152.07	$152.05	$152.10
Purchase #4	$167.89	12.356%	$188.6345	$188.63	$188.65	$188.60
Purchase #5	$52.31	5.241%	$55.0516	$55.05	$55.05	$55.10
Purchase #6	$210.63	8.504%	$228.542	$228.54	$228.55	$228.50
Purchase #7	$30.47	7.564%	$32.7748	$32.77	$32.75	$32.80
7 purchase totals =	$809.32		$888.9946	$888.98	$889.00	$889.00