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	$6.73	11.578%	$7.5092	$7.51	$7.50	$7.50
Purchase #2	$193.37	6.478%	$205.8965	$205.90	$205.90	$205.90
Purchase #3	$82.51	13.474%	$93.6274	$93.63	$93.65	$93.60
Purchase #4	$191.38	12.341%	$214.9982	$215.00	$215.00	$215.00
Purchase #5	$88.52	7.194%	$94.8881	$94.89	$94.90	$94.90
Purchase #6	$182.79	4.641%	$191.2733	$191.27	$191.25	$191.30
Purchase #7	$150.41	5.666%	$158.9322	$158.93	$158.95	$158.90
7 purchase totals =	$895.71		$967.1249	$967.13	$967.15	$967.10