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	$249.49	8.786%	$271.4102	$271.41	$271.40	$271.40
Purchase #2	$48.65	11.847%	$54.4136	$54.41	$54.40	$54.40
Purchase #3	$56.53	9.369%	$61.8263	$61.83	$61.85	$61.80
Purchase #4	$82.55	4.858%	$86.5603	$86.56	$86.55	$86.60
Purchase #5	$168.75	6.148%	$179.1248	$179.12	$179.10	$179.10
Purchase #6	$213.77	6.563%	$227.7997	$227.80	$227.80	$227.80
Purchase #7	$48.41	7.234%	$51.912	$51.91	$51.90	$51.90
7 purchase totals =	$868.15		$933.0469	$933.04	$933.00	$933.00