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	$79.28	3.704%	$82.2165	$82.22	$82.20	$82.20
Purchase #2	$120.38	6.229%	$127.8785	$127.88	$127.90	$127.90
Purchase #3	$98.79	8.806%	$107.4894	$107.49	$107.50	$107.50
Purchase #4	$52.97	8.605%	$57.5281	$57.53	$57.55	$57.50
Purchase #5	$164.99	12.388%	$185.429	$185.43	$185.45	$185.40
Purchase #6	$174.78	3.138%	$180.2646	$180.26	$180.25	$180.30
Purchase #7	$127.69	7.308%	$137.0216	$137.02	$137.00	$137.00
7 purchase totals =	$818.88		$877.8277	$877.83	$877.85	$877.80