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	$75.94	8.631%	$82.4944	$82.49	$82.50	$82.50
Purchase #2	$130.33	10.813%	$144.4226	$144.42	$144.40	$144.40
Purchase #3	$107.65	4.391%	$112.3769	$112.38	$112.40	$112.40
Purchase #4	$89.99	9.703%	$98.7217	$98.72	$98.70	$98.70
Purchase #5	$113.63	8.702%	$123.5181	$123.52	$123.50	$123.50
Purchase #6	$103.26	9.309%	$112.8725	$112.87	$112.85	$112.90
Purchase #7	$205.69	6.733%	$219.5391	$219.54	$219.55	$219.50
7 purchase totals =	$826.49		$893.9453	$893.94	$893.90	$893.90