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	$40.50	9.743%	$44.4459	$44.45	$44.45	$44.40
Purchase #2	$78.84	12.563%	$88.7447	$88.74	$88.75	$88.70
Purchase #3	$18.95	7.656%	$20.4008	$20.40	$20.40	$20.40
Purchase #4	$173.41	8.744%	$188.573	$188.57	$188.55	$188.60
Purchase #5	$127.30	11.105%	$141.4367	$141.44	$141.45	$141.40
Purchase #6	$101.27	7.673%	$109.0404	$109.04	$109.05	$109.00
Purchase #7	$108.72	7.119%	$116.4598	$116.46	$116.45	$116.50
7 purchase totals =	$648.99		$709.1013	$709.10	$709.10	$709.00