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	$239.71	6.591%	$255.5093	$255.51	$255.50	$255.50
Purchase #2	$137.39	9.469%	$150.3995	$150.40	$150.40	$150.40
Purchase #3	$66.65	13.613%	$75.7231	$75.72	$75.70	$75.70
Purchase #4	$50.42	10.162%	$55.5437	$55.54	$55.55	$55.50
Purchase #5	$205.34	10.374%	$226.642	$226.64	$226.65	$226.60
Purchase #6	$72.32	13.390%	$82.0036	$82.00	$82.00	$82.00
Purchase #7	$159.31	3.190%	$164.392	$164.39	$164.40	$164.40
7 purchase totals =	$931.14		$1,010.2132	$1,010.20	$1,010.20	$1,010.10