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	$5.40	6.848%	$5.7698	$5.77	$5.75	$5.80
Purchase #2	$215.82	6.768%	$230.4267	$230.43	$230.45	$230.40
Purchase #3	$245.83	3.818%	$255.2158	$255.22	$255.20	$255.20
Purchase #4	$39.94	10.415%	$44.0998	$44.10	$44.10	$44.10
Purchase #5	$179.88	6.649%	$191.8402	$191.84	$191.85	$191.80
Purchase #6	$86.69	3.173%	$89.4407	$89.44	$89.45	$89.40
Purchase #7	$157.72	5.353%	$166.1628	$166.16	$166.15	$166.20
7 purchase totals =	$931.28		$982.9558	$982.96	$982.95	$982.90