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	$131.50	11.528%	$146.6593	$146.66	$146.65	$146.70
Purchase #2	$147.72	11.485%	$164.6856	$164.69	$164.70	$164.70
Purchase #3	$25.28	13.841%	$28.779	$28.78	$28.80	$28.80
Purchase #4	$247.89	11.329%	$275.9735	$275.97	$275.95	$276.00
Purchase #5	$9.66	4.434%	$10.0883	$10.09	$10.10	$10.10
Purchase #6	$232.81	7.759%	$250.8737	$250.87	$250.85	$250.90
Purchase #7	$122.62	7.573%	$131.906	$131.91	$131.90	$131.90
7 purchase totals =	$917.48		$1,008.9654	$1,008.97	$1,008.95	$1,009.10