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	$222.38	12.590%	$250.3776	$250.38	$250.40	$250.40
Purchase #2	$144.92	5.484%	$152.8674	$152.87	$152.85	$152.90
Purchase #3	$72.66	9.321%	$79.4326	$79.43	$79.45	$79.40
Purchase #4	$33.84	10.314%	$37.3303	$37.33	$37.35	$37.30
Purchase #5	$133.53	4.446%	$139.4667	$139.47	$139.45	$139.50
Purchase #6	$125.69	3.441%	$130.015	$130.02	$130.00	$130.00
Purchase #7	$47.58	8.384%	$51.5691	$51.57	$51.55	$51.60
7 purchase totals =	$780.60		$841.0587	$841.07	$841.05	$841.10