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	$139.57	7.423%	$149.9303	$149.93	$149.95	$149.90
Purchase #2	$226.36	12.275%	$254.1457	$254.15	$254.15	$254.10
Purchase #3	$167.59	3.184%	$172.9261	$172.93	$172.95	$172.90
Purchase #4	$102.70	9.743%	$112.7061	$112.71	$112.70	$112.70
Purchase #5	$164.86	11.483%	$183.7909	$183.79	$183.80	$183.80
Purchase #6	$54.38	6.540%	$57.9365	$57.94	$57.95	$57.90
Purchase #7	$39.55	6.472%	$42.1097	$42.11	$42.10	$42.10
7 purchase totals =	$895.01		$973.5453	$973.56	$973.60	$973.40