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	$105.56	13.539%	$119.8518	$119.85	$119.85	$119.90
Purchase #2	$131.57	7.604%	$141.5746	$141.57	$141.55	$141.60
Purchase #3	$59.85	5.745%	$63.2884	$63.29	$63.30	$63.30
Purchase #4	$123.70	3.225%	$127.6893	$127.69	$127.70	$127.70
Purchase #5	$153.59	10.336%	$169.4651	$169.47	$169.45	$169.50
Purchase #6	$76.96	7.102%	$82.4257	$82.43	$82.45	$82.40
Purchase #7	$123.33	8.616%	$133.9561	$133.96	$133.95	$134.00
7 purchase totals =	$774.56		$838.2510	$838.26	$838.25	$838.40