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	$147.73	11.500%	$164.719	$164.72	$164.70	$164.70
Purchase #2	$91.34	9.583%	$100.0931	$100.09	$100.10	$100.10
Purchase #3	$78.29	10.491%	$86.5034	$86.50	$86.50	$86.50
Purchase #4	$248.29	6.577%	$264.62	$264.62	$264.60	$264.60
Purchase #5	$94.63	11.750%	$105.749	$105.75	$105.75	$105.70
Purchase #6	$65.97	7.242%	$70.7475	$70.75	$70.75	$70.70
Purchase #7	$50.69	13.445%	$57.5053	$57.51	$57.50	$57.50
7 purchase totals =	$776.94		$849.9373	$849.94	$849.90	$849.80