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	$175.35	8.249%	$189.8146	$189.81	$189.80	$189.80
Purchase #2	$112.52	5.611%	$118.8335	$118.83	$118.85	$118.80
Purchase #3	$71.56	5.504%	$75.4987	$75.50	$75.50	$75.50
Purchase #4	$148.65	12.431%	$167.1287	$167.13	$167.15	$167.10
Purchase #5	$64.96	8.874%	$70.7246	$70.72	$70.70	$70.70
Purchase #6	$141.50	6.641%	$150.897	$150.90	$150.90	$150.90
Purchase #7	$99.96	3.874%	$103.8325	$103.83	$103.85	$103.80
7 purchase totals =	$814.50		$876.7296	$876.72	$876.75	$876.60