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	$81.82	8.671%	$88.9146	$88.91	$88.90	$88.90
Purchase #2	$136.85	3.157%	$141.1704	$141.17	$141.15	$141.20
Purchase #3	$112.83	9.756%	$123.8377	$123.84	$123.85	$123.80
Purchase #4	$101.25	9.660%	$111.0308	$111.03	$111.05	$111.00
Purchase #5	$30.74	5.581%	$32.4556	$32.46	$32.45	$32.50
Purchase #6	$238.43	9.234%	$260.4466	$260.45	$260.45	$260.40
Purchase #7	$241.33	7.332%	$259.0243	$259.02	$259.00	$259.00
7 purchase totals =	$943.25		$1,016.8800	$1,016.88	$1,016.85	$1,016.80