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	$82.98	9.490%	$90.8548	$90.85	$90.85	$90.90
Purchase #2	$243.39	6.781%	$259.8943	$259.89	$259.90	$259.90
Purchase #3	$45.96	11.614%	$51.2978	$51.30	$51.30	$51.30
Purchase #4	$130.52	10.278%	$143.9348	$143.93	$143.95	$143.90
Purchase #5	$230.58	12.355%	$259.0682	$259.07	$259.05	$259.10
Purchase #6	$164.29	4.115%	$171.0505	$171.05	$171.05	$171.10
Purchase #7	$235.75	10.432%	$260.3434	$260.34	$260.35	$260.30
7 purchase totals =	$1,133.47		$1,236.4438	$1,236.43	$1,236.45	$1,236.50