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	$25.83	10.607%	$28.5698	$28.57	$28.55	$28.60
Purchase #2	$162.26	10.792%	$179.7711	$179.77	$179.75	$179.80
Purchase #3	$180.53	4.409%	$188.4896	$188.49	$188.50	$188.50
Purchase #4	$98.33	10.631%	$108.7835	$108.78	$108.80	$108.80
Purchase #5	$40.34	13.727%	$45.8775	$45.88	$45.90	$45.90
Purchase #6	$105.37	5.312%	$110.9673	$110.97	$110.95	$111.00
Purchase #7	$110.45	3.583%	$114.4074	$114.41	$114.40	$114.40
7 purchase totals =	$723.11		$776.8662	$776.87	$776.85	$777.00