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	$16.27	6.543%	$17.3345	$17.33	$17.35	$17.30
Purchase #2	$217.91	11.479%	$242.9239	$242.92	$242.90	$242.90
Purchase #3	$19.86	12.665%	$22.3753	$22.38	$22.40	$22.40
Purchase #4	$70.64	11.587%	$78.8251	$78.83	$78.85	$78.80
Purchase #5	$21.27	6.806%	$22.7176	$22.72	$22.70	$22.70
Purchase #6	$249.33	6.292%	$265.0178	$265.02	$265.00	$265.00
Purchase #7	$18.77	9.803%	$20.61	$20.61	$20.60	$20.60
7 purchase totals =	$614.05		$669.8042	$669.81	$669.80	$669.70