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	$242.31	12.824%	$273.3838	$273.38	$273.40	$273.40
Purchase #2	$161.97	3.430%	$167.5256	$167.53	$167.55	$167.50
Purchase #3	$92.94	13.818%	$105.7824	$105.78	$105.80	$105.80
Purchase #4	$116.60	12.462%	$131.1307	$131.13	$131.15	$131.10
Purchase #5	$196.93	11.569%	$219.7128	$219.71	$219.70	$219.70
Purchase #6	$239.83	7.489%	$257.7909	$257.79	$257.80	$257.80
Purchase #7	$233.45	3.175%	$240.862	$240.86	$240.85	$240.90
7 purchase totals =	$1,284.03		$1,396.1882	$1,396.18	$1,396.25	$1,396.20