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	$88.90	13.364%	$100.7806	$100.78	$100.80	$100.80
Purchase #2	$186.94	12.545%	$210.3916	$210.39	$210.40	$210.40
Purchase #3	$150.49	4.272%	$156.9189	$156.92	$156.90	$156.90
Purchase #4	$123.45	6.821%	$131.8705	$131.87	$131.85	$131.90
Purchase #5	$122.57	3.195%	$126.4861	$126.49	$126.50	$126.50
Purchase #6	$56.48	8.536%	$61.3011	$61.30	$61.30	$61.30
Purchase #7	$199.81	7.620%	$215.0355	$215.04	$215.05	$215.00
7 purchase totals =	$928.64		$1,002.7843	$1,002.79	$1,002.80	$1,002.80