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	$101.87	10.718%	$112.7884	$112.79	$112.80	$112.80
Purchase #2	$47.77	11.596%	$53.3094	$53.31	$53.30	$53.30
Purchase #3	$111.44	6.309%	$118.4707	$118.47	$118.45	$118.50
Purchase #4	$148.52	3.279%	$153.39	$153.39	$153.40	$153.40
Purchase #5	$31.95	9.670%	$35.0396	$35.04	$35.05	$35.00
Purchase #6	$158.89	4.477%	$166.0035	$166.00	$166.00	$166.00
Purchase #7	$78.59	3.123%	$81.0444	$81.04	$81.05	$81.00
7 purchase totals =	$679.03		$720.0460	$720.04	$720.05	$720.00