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	$60.76	12.582%	$68.4048	$68.40	$68.40	$68.40
Purchase #2	$226.86	10.756%	$251.2611	$251.26	$251.25	$251.30
Purchase #3	$182.61	7.454%	$196.2217	$196.22	$196.20	$196.20
Purchase #4	$114.61	13.806%	$130.4331	$130.43	$130.45	$130.40
Purchase #5	$17.98	11.808%	$20.1031	$20.10	$20.10	$20.10
Purchase #6	$31.72	4.711%	$33.2143	$33.21	$33.20	$33.20
Purchase #7	$250.88	11.872%	$280.6645	$280.66	$280.65	$280.70
7 purchase totals =	$885.42		$980.3026	$980.28	$980.25	$980.30