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	$83.86	11.103%	$93.171	$93.17	$93.15	$93.20
Purchase #2	$93.99	12.177%	$105.4352	$105.44	$105.45	$105.40
Purchase #3	$18.79	3.796%	$19.5033	$19.50	$19.50	$19.50
Purchase #4	$53.55	3.359%	$55.3487	$55.35	$55.35	$55.30
Purchase #5	$79.40	11.811%	$88.7779	$88.78	$88.80	$88.80
Purchase #6	$81.94	10.764%	$90.76	$90.76	$90.75	$90.80
Purchase #7	$107.58	3.613%	$111.4669	$111.47	$111.45	$111.50
7 purchase totals =	$519.11		$564.4630	$564.47	$564.45	$564.50