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	$26.96	7.340%	$28.9389	$28.94	$28.95	$28.90
Purchase #2	$45.73	9.384%	$50.0213	$50.02	$50.00	$50.00
Purchase #3	$164.38	13.852%	$187.1499	$187.15	$187.15	$187.10
Purchase #4	$48.50	7.660%	$52.2151	$52.22	$52.20	$52.20
Purchase #5	$64.38	11.516%	$71.794	$71.79	$71.80	$71.80
Purchase #6	$246.46	13.556%	$279.8701	$279.87	$279.85	$279.90
Purchase #7	$186.32	7.682%	$200.6331	$200.63	$200.65	$200.60
7 purchase totals =	$782.73		$870.6224	$870.62	$870.60	$870.50