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	$174.84	6.151%	$185.5944	$185.59	$185.60	$185.60
Purchase #2	$166.25	5.692%	$175.713	$175.71	$175.70	$175.70
Purchase #3	$187.38	4.606%	$196.0107	$196.01	$196.00	$196.00
Purchase #4	$164.86	13.779%	$187.5761	$187.58	$187.60	$187.60
Purchase #5	$42.60	8.620%	$46.2721	$46.27	$46.25	$46.30
Purchase #6	$179.39	11.372%	$199.7902	$199.79	$199.80	$199.80
Purchase #7	$5.92	6.793%	$6.3221	$6.32	$6.30	$6.30
7 purchase totals =	$921.24		$997.2786	$997.27	$997.25	$997.30