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	$70.76	6.600%	$75.4302	$75.43	$75.45	$75.40
Purchase #2	$82.35	12.194%	$92.3918	$92.39	$92.40	$92.40
Purchase #3	$234.64	9.399%	$256.6938	$256.69	$256.70	$256.70
Purchase #4	$48.93	12.112%	$54.8564	$54.86	$54.85	$54.90
Purchase #5	$104.93	8.480%	$113.8281	$113.83	$113.85	$113.80
Purchase #6	$64.88	11.632%	$72.4268	$72.43	$72.45	$72.40
Purchase #7	$194.43	5.631%	$205.3784	$205.38	$205.40	$205.40
7 purchase totals =	$800.92		$871.0055	$871.01	$871.10	$871.00