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	$47.42	9.259%	$51.8106	$51.81	$51.80	$51.80
Purchase #2	$25.56	11.847%	$28.5881	$28.59	$28.60	$28.60
Purchase #3	$39.74	9.265%	$43.4219	$43.42	$43.40	$43.40
Purchase #4	$195.42	7.540%	$210.1547	$210.15	$210.15	$210.20
Purchase #5	$153.30	11.743%	$171.302	$171.30	$171.30	$171.30
Purchase #6	$42.52	10.631%	$47.0403	$47.04	$47.05	$47.00
Purchase #7	$112.76	12.777%	$127.1673	$127.17	$127.15	$127.20
7 purchase totals =	$616.72		$679.4849	$679.48	$679.45	$679.50