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	$69.74	12.469%	$78.4359	$78.44	$78.45	$78.40
Purchase #2	$123.80	10.248%	$136.487	$136.49	$136.50	$136.50
Purchase #3	$73.78	11.397%	$82.1887	$82.19	$82.20	$82.20
Purchase #4	$164.57	9.341%	$179.9425	$179.94	$179.95	$179.90
Purchase #5	$108.52	10.694%	$120.1251	$120.13	$120.15	$120.10
Purchase #6	$76.29	3.124%	$78.6733	$78.67	$78.65	$78.70
Purchase #7	$154.62	9.551%	$169.3878	$169.39	$169.40	$169.40
7 purchase totals =	$771.32		$845.2403	$845.25	$845.30	$845.20