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	$30.88	5.445%	$32.5614	$32.56	$32.55	$32.60
Purchase #2	$123.67	11.391%	$137.7572	$137.76	$137.75	$137.80
Purchase #3	$150.51	4.465%	$157.2303	$157.23	$157.25	$157.20
Purchase #4	$138.72	12.329%	$155.8228	$155.82	$155.80	$155.80
Purchase #5	$114.45	8.665%	$124.3671	$124.37	$124.35	$124.40
Purchase #6	$66.33	3.869%	$68.8963	$68.90	$68.90	$68.90
Purchase #7	$148.59	13.114%	$168.0761	$168.08	$168.10	$168.10
7 purchase totals =	$773.15		$844.7112	$844.72	$844.70	$844.80