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	$157.96	12.757%	$178.111	$178.11	$178.10	$178.10
Purchase #2	$100.38	3.642%	$104.0358	$104.04	$104.05	$104.00
Purchase #3	$194.28	5.321%	$204.6176	$204.62	$204.60	$204.60
Purchase #4	$37.63	6.856%	$40.2099	$40.21	$40.20	$40.20
Purchase #5	$59.39	13.726%	$67.5419	$67.54	$67.55	$67.50
Purchase #6	$134.96	6.346%	$143.5246	$143.52	$143.50	$143.50
Purchase #7	$162.94	10.366%	$179.8304	$179.83	$179.85	$179.80
7 purchase totals =	$847.54		$917.8712	$917.87	$917.85	$917.70