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	$32.71	7.766%	$35.2503	$35.25	$35.25	$35.30
Purchase #2	$117.89	6.109%	$125.0919	$125.09	$125.10	$125.10
Purchase #3	$101.73	9.768%	$111.667	$111.67	$111.65	$111.70
Purchase #4	$97.86	13.811%	$111.3754	$111.38	$111.40	$111.40
Purchase #5	$101.80	7.417%	$109.3505	$109.35	$109.35	$109.40
Purchase #6	$51.76	12.174%	$58.0613	$58.06	$58.05	$58.10
Purchase #7	$107.89	5.262%	$113.5672	$113.57	$113.55	$113.60
7 purchase totals =	$611.64		$664.3636	$664.37	$664.35	$664.60