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	$227.93	3.555%	$236.0329	$236.03	$236.05	$236.00
Purchase #2	$72.25	8.495%	$78.3876	$78.39	$78.40	$78.40
Purchase #3	$156.43	11.554%	$174.5039	$174.50	$174.50	$174.50
Purchase #4	$84.61	5.859%	$89.5673	$89.57	$89.55	$89.60
Purchase #5	$95.47	13.799%	$108.6439	$108.64	$108.65	$108.60
Purchase #6	$75.79	13.331%	$85.8936	$85.89	$85.90	$85.90
Purchase #7	$53.64	10.632%	$59.343	$59.34	$59.35	$59.30
7 purchase totals =	$766.12		$832.3722	$832.36	$832.40	$832.30