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	$13.94	6.729%	$14.878	$14.88	$14.90	$14.90
Purchase #2	$67.48	12.759%	$76.0898	$76.09	$76.10	$76.10
Purchase #3	$70.69	11.432%	$78.7713	$78.77	$78.75	$78.80
Purchase #4	$159.48	8.102%	$172.4011	$172.40	$172.40	$172.40
Purchase #5	$205.40	10.569%	$227.1087	$227.11	$227.10	$227.10
Purchase #6	$14.83	10.544%	$16.3937	$16.39	$16.40	$16.40
Purchase #7	$71.93	11.581%	$80.2602	$80.26	$80.25	$80.30
7 purchase totals =	$603.75		$665.9028	$665.90	$665.90	$666.00