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	$31.82	13.246%	$36.0349	$36.03	$36.05	$36.00
Purchase #2	$51.79	5.510%	$54.6436	$54.64	$54.65	$54.60
Purchase #3	$123.47	11.424%	$137.5752	$137.58	$137.60	$137.60
Purchase #4	$100.96	13.253%	$114.3402	$114.34	$114.35	$114.30
Purchase #5	$173.31	3.286%	$179.005	$179.01	$179.00	$179.00
Purchase #6	$58.96	5.213%	$62.0336	$62.03	$62.05	$62.00
Purchase #7	$141.90	6.645%	$151.3293	$151.33	$151.35	$151.30
7 purchase totals =	$682.21		$734.9618	$734.96	$735.05	$734.80