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	$55.59	13.430%	$63.0557	$63.06	$63.05	$63.10
Purchase #2	$115.48	10.682%	$127.8156	$127.82	$127.80	$127.80
Purchase #3	$167.71	3.245%	$173.1522	$173.15	$173.15	$173.20
Purchase #4	$120.77	7.155%	$129.4111	$129.41	$129.40	$129.40
Purchase #5	$39.49	10.728%	$43.7265	$43.73	$43.75	$43.70
Purchase #6	$113.86	12.246%	$127.8033	$127.80	$127.80	$127.80
Purchase #7	$242.82	5.635%	$256.5029	$256.50	$256.50	$256.50
7 purchase totals =	$855.72		$921.4673	$921.47	$921.45	$921.50