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	$76.43	9.108%	$83.3912	$83.39	$83.40	$83.40
Purchase #2	$19.88	4.580%	$20.7905	$20.79	$20.80	$20.80
Purchase #3	$125.64	8.420%	$136.2189	$136.22	$136.20	$136.20
Purchase #4	$166.34	5.745%	$175.8962	$175.90	$175.90	$175.90
Purchase #5	$38.90	8.687%	$42.2792	$42.28	$42.30	$42.30
Purchase #6	$96.70	3.677%	$100.2557	$100.26	$100.25	$100.30
Purchase #7	$37.79	11.757%	$42.233	$42.23	$42.25	$42.20
7 purchase totals =	$561.68		$601.0647	$601.07	$601.10	$601.10