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	$34.70	8.673%	$37.7095	$37.71	$37.70	$37.70
Purchase #2	$233.93	6.831%	$249.9098	$249.91	$249.90	$249.90
Purchase #3	$123.54	11.619%	$137.8941	$137.89	$137.90	$137.90
Purchase #4	$125.88	3.327%	$130.068	$130.07	$130.05	$130.10
Purchase #5	$137.72	3.530%	$142.5815	$142.58	$142.60	$142.60
Purchase #6	$249.68	12.493%	$280.8725	$280.87	$280.85	$280.90
Purchase #7	$189.85	9.125%	$207.1738	$207.17	$207.15	$207.20
7 purchase totals =	$1,095.30		$1,186.2092	$1,186.20	$1,186.15	$1,186.30