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	$91.67	10.830%	$101.5979	$101.60	$101.60	$101.60
Purchase #2	$161.32	12.596%	$181.6399	$181.64	$181.65	$181.60
Purchase #3	$19.80	6.308%	$21.049	$21.05	$21.05	$21.00
Purchase #4	$29.64	8.266%	$32.09	$32.09	$32.10	$32.10
Purchase #5	$136.37	3.805%	$141.5589	$141.56	$141.55	$141.60
Purchase #6	$45.83	10.121%	$50.4685	$50.47	$50.45	$50.50
Purchase #7	$116.26	3.162%	$119.9361	$119.94	$119.95	$119.90
7 purchase totals =	$600.89		$648.3403	$648.35	$648.35	$648.30