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	$238.40	8.820%	$259.4269	$259.43	$259.45	$259.40
Purchase #2	$222.83	11.218%	$247.8271	$247.83	$247.85	$247.80
Purchase #3	$250.79	10.151%	$276.2477	$276.25	$276.25	$276.20
Purchase #4	$95.48	10.120%	$105.1426	$105.14	$105.15	$105.10
Purchase #5	$15.75	6.482%	$16.7709	$16.77	$16.75	$16.80
Purchase #6	$45.52	7.311%	$48.848	$48.85	$48.85	$48.80
Purchase #7	$57.44	3.578%	$59.4952	$59.50	$59.50	$59.50
7 purchase totals =	$926.21		$1,013.7584	$1,013.77	$1,013.80	$1,013.60