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	$93.86	11.192%	$104.3648	$104.36	$104.35	$104.40
Purchase #2	$226.44	5.529%	$238.9599	$238.96	$238.95	$239.00
Purchase #3	$77.47	7.303%	$83.1276	$83.13	$83.15	$83.10
Purchase #4	$90.72	10.237%	$100.007	$100.01	$100.00	$100.00
Purchase #5	$153.66	12.124%	$172.2897	$172.29	$172.30	$172.30
Purchase #6	$89.49	10.795%	$99.1504	$99.15	$99.15	$99.20
Purchase #7	$178.65	11.162%	$198.5909	$198.59	$198.60	$198.60
7 purchase totals =	$910.29		$996.4903	$996.49	$996.50	$996.60