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	$85.86	4.320%	$89.5692	$89.57	$89.55	$89.60
Purchase #2	$154.81	10.426%	$170.9505	$170.95	$170.95	$171.00
Purchase #3	$246.91	3.202%	$254.8161	$254.82	$254.80	$254.80
Purchase #4	$170.69	4.158%	$177.7873	$177.79	$177.80	$177.80
Purchase #5	$166.60	11.244%	$185.3325	$185.33	$185.35	$185.30
Purchase #6	$78.44	10.705%	$86.837	$86.84	$86.85	$86.80
Purchase #7	$149.57	10.166%	$164.7753	$164.78	$164.80	$164.80
7 purchase totals =	$1,052.88		$1,130.0679	$1,130.08	$1,130.10	$1,130.10