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	$75.51	3.457%	$78.1204	$78.12	$78.10	$78.10
Purchase #2	$99.93	9.155%	$109.0786	$109.08	$109.10	$109.10
Purchase #3	$123.53	11.697%	$137.9793	$137.98	$138.00	$138.00
Purchase #4	$127.34	5.278%	$134.061	$134.06	$134.05	$134.10
Purchase #5	$81.50	3.741%	$84.5489	$84.55	$84.55	$84.50
Purchase #6	$144.73	4.438%	$151.1531	$151.15	$151.15	$151.20
Purchase #7	$63.46	6.244%	$67.4224	$67.42	$67.40	$67.40
7 purchase totals =	$716.00		$762.3637	$762.36	$762.35	$762.40