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	$90.43	6.852%	$96.6263	$96.63	$96.65	$96.60
Purchase #2	$213.97	6.801%	$228.5221	$228.52	$228.50	$228.50
Purchase #3	$182.34	3.350%	$188.4484	$188.45	$188.45	$188.40
Purchase #4	$90.74	9.607%	$99.4574	$99.46	$99.45	$99.50
Purchase #5	$103.58	9.243%	$113.1539	$113.15	$113.15	$113.20
Purchase #6	$103.81	9.277%	$113.4405	$113.44	$113.45	$113.40
Purchase #7	$130.51	11.331%	$145.2981	$145.30	$145.30	$145.30
7 purchase totals =	$915.38		$984.9467	$984.95	$984.95	$984.90