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	$75.35	4.326%	$78.6096	$78.61	$78.60	$78.60
Purchase #2	$83.51	7.260%	$89.5728	$89.57	$89.55	$89.60
Purchase #3	$34.97	6.219%	$37.1448	$37.14	$37.15	$37.10
Purchase #4	$232.32	12.633%	$261.669	$261.67	$261.65	$261.70
Purchase #5	$82.39	7.549%	$88.6096	$88.61	$88.60	$88.60
Purchase #6	$11.47	9.560%	$12.5665	$12.57	$12.55	$12.60
Purchase #7	$58.66	7.786%	$63.2273	$63.23	$63.25	$63.20
7 purchase totals =	$578.67		$631.3996	$631.40	$631.35	$631.40