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	$89.79	12.327%	$100.8584	$100.86	$100.85	$100.90
Purchase #2	$34.27	11.639%	$38.2587	$38.26	$38.25	$38.30
Purchase #3	$146.68	13.349%	$166.2603	$166.26	$166.25	$166.30
Purchase #4	$171.41	11.443%	$191.0244	$191.02	$191.00	$191.00
Purchase #5	$176.38	12.329%	$198.1259	$198.13	$198.15	$198.10
Purchase #6	$247.89	12.770%	$279.5456	$279.55	$279.55	$279.50
Purchase #7	$172.92	6.312%	$183.8347	$183.83	$183.85	$183.80
7 purchase totals =	$1,039.34		$1,157.9080	$1,157.91	$1,157.90	$1,157.90