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	$83.52	7.184%	$89.5201	$89.52	$89.50	$89.50
Purchase #2	$178.27	7.360%	$191.3907	$191.39	$191.40	$191.40
Purchase #3	$153.64	9.513%	$168.2558	$168.26	$168.25	$168.30
Purchase #4	$188.85	11.587%	$210.732	$210.73	$210.75	$210.70
Purchase #5	$238.66	5.860%	$252.6455	$252.65	$252.65	$252.60
Purchase #6	$136.70	6.243%	$145.2342	$145.23	$145.25	$145.20
Purchase #7	$16.67	11.506%	$18.5881	$18.59	$18.60	$18.60
7 purchase totals =	$996.31		$1,076.3664	$1,076.37	$1,076.40	$1,076.30