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	$44.60	12.223%	$50.0515	$50.05	$50.05	$50.10
Purchase #2	$151.97	9.409%	$166.2689	$166.27	$166.25	$166.30
Purchase #3	$55.60	6.124%	$59.0049	$59.00	$59.00	$59.00
Purchase #4	$88.48	13.255%	$100.208	$100.21	$100.20	$100.20
Purchase #5	$87.55	11.796%	$97.8774	$97.88	$97.90	$97.90
Purchase #6	$148.63	9.267%	$162.4035	$162.40	$162.40	$162.40
Purchase #7	$137.67	6.487%	$146.6007	$146.60	$146.60	$146.60
7 purchase totals =	$714.50		$782.4149	$782.41	$782.40	$782.50