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	$139.72	5.729%	$147.7246	$147.72	$147.70	$147.70
Purchase #2	$51.87	7.802%	$55.9169	$55.92	$55.90	$55.90
Purchase #3	$64.78	11.847%	$72.4545	$72.45	$72.45	$72.50
Purchase #4	$134.44	3.398%	$139.0083	$139.01	$139.00	$139.00
Purchase #5	$55.81	7.247%	$59.8546	$59.85	$59.85	$59.90
Purchase #6	$77.60	4.721%	$81.2635	$81.26	$81.25	$81.30
Purchase #7	$80.37	5.701%	$84.9519	$84.95	$84.95	$85.00
7 purchase totals =	$604.59		$641.1743	$641.16	$641.10	$641.30