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	$250.97	7.778%	$270.4904	$270.49	$270.50	$270.50
Purchase #2	$131.82	9.482%	$144.3192	$144.32	$144.30	$144.30
Purchase #3	$98.34	4.610%	$102.8735	$102.87	$102.85	$102.90
Purchase #4	$155.43	7.630%	$167.2893	$167.29	$167.30	$167.30
Purchase #5	$164.72	13.490%	$186.9407	$186.94	$186.95	$186.90
Purchase #6	$178.34	8.816%	$194.0625	$194.06	$194.05	$194.10
Purchase #7	$151.75	3.844%	$157.5833	$157.58	$157.60	$157.60
7 purchase totals =	$1,131.37		$1,223.5589	$1,223.55	$1,223.55	$1,223.60