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	$61.86	12.550%	$69.6234	$69.62	$69.60	$69.60
Purchase #2	$173.25	6.175%	$183.9482	$183.95	$183.95	$183.90
Purchase #3	$48.28	11.540%	$53.8515	$53.85	$53.85	$53.90
Purchase #4	$141.57	10.795%	$156.8525	$156.85	$156.85	$156.90
Purchase #5	$137.49	10.482%	$151.9017	$151.90	$151.90	$151.90
Purchase #6	$147.60	13.371%	$167.3356	$167.34	$167.35	$167.30
Purchase #7	$59.90	3.705%	$62.1193	$62.12	$62.10	$62.10
7 purchase totals =	$769.95		$845.6322	$845.63	$845.60	$845.60