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	$79.90	4.151%	$83.2166	$83.22	$83.20	$83.20
Purchase #2	$145.74	12.255%	$163.6004	$163.60	$163.60	$163.60
Purchase #3	$42.31	12.120%	$47.438	$47.44	$47.45	$47.40
Purchase #4	$222.54	3.618%	$230.5915	$230.59	$230.60	$230.60
Purchase #5	$166.56	3.166%	$171.8333	$171.83	$171.85	$171.80
Purchase #6	$40.66	11.819%	$45.4656	$45.47	$45.45	$45.50
Purchase #7	$196.74	10.176%	$216.7603	$216.76	$216.75	$216.80
7 purchase totals =	$894.45		$958.9057	$958.91	$958.90	$958.90