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	$14.71	7.609%	$15.8293	$15.83	$15.85	$15.80
Purchase #2	$91.27	7.811%	$98.3991	$98.40	$98.40	$98.40
Purchase #3	$92.44	7.787%	$99.6383	$99.64	$99.65	$99.60
Purchase #4	$162.45	10.419%	$179.3757	$179.38	$179.40	$179.40
Purchase #5	$205.86	12.384%	$231.3537	$231.35	$231.35	$231.40
Purchase #6	$86.38	11.156%	$96.0166	$96.02	$96.00	$96.00
Purchase #7	$111.70	10.842%	$123.8105	$123.81	$123.80	$123.80
7 purchase totals =	$764.81		$844.4232	$844.43	$844.45	$844.40