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	$156.60	11.175%	$174.1001	$174.10	$174.10	$174.10
Purchase #2	$158.27	4.230%	$164.9648	$164.96	$164.95	$165.00
Purchase #3	$196.50	10.654%	$217.4351	$217.44	$217.45	$217.40
Purchase #4	$107.46	9.426%	$117.5892	$117.59	$117.60	$117.60
Purchase #5	$71.37	10.427%	$78.8117	$78.81	$78.80	$78.80
Purchase #6	$51.31	12.796%	$57.8756	$57.88	$57.90	$57.90
Purchase #7	$171.26	12.111%	$192.0013	$192.00	$192.00	$192.00
7 purchase totals =	$912.77		$1,002.7778	$1,002.78	$1,002.80	$1,002.80