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	$147.61	12.848%	$166.5749	$166.57	$166.55	$166.60
Purchase #2	$20.51	7.641%	$22.0772	$22.08	$22.10	$22.10
Purchase #3	$215.43	4.349%	$224.7991	$224.80	$224.80	$224.80
Purchase #4	$132.76	3.658%	$137.6164	$137.62	$137.60	$137.60
Purchase #5	$25.25	5.194%	$26.5615	$26.56	$26.55	$26.60
Purchase #6	$137.49	5.416%	$144.9365	$144.94	$144.95	$144.90
Purchase #7	$106.84	4.713%	$111.8754	$111.88	$111.90	$111.90
7 purchase totals =	$785.89		$834.4410	$834.45	$834.45	$834.50