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	$73.99	11.626%	$82.5921	$82.59	$82.60	$82.60
Purchase #2	$44.96	3.304%	$46.4455	$46.45	$46.45	$46.40
Purchase #3	$98.56	10.677%	$109.0833	$109.08	$109.10	$109.10
Purchase #4	$5.35	9.464%	$5.8563	$5.86	$5.85	$5.90
Purchase #5	$97.86	5.367%	$103.1121	$103.11	$103.10	$103.10
Purchase #6	$40.56	11.773%	$45.3351	$45.34	$45.35	$45.30
Purchase #7	$142.68	4.846%	$149.5943	$149.59	$149.60	$149.60
7 purchase totals =	$503.96		$542.0187	$542.02	$542.05	$542.00