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	$238.48	4.850%	$250.0463	$250.05	$250.05	$250.00
Purchase #2	$87.81	13.308%	$99.4958	$99.50	$99.50	$99.50
Purchase #3	$95.29	3.544%	$98.6671	$98.67	$98.65	$98.70
Purchase #4	$45.83	11.351%	$51.0322	$51.03	$51.05	$51.00
Purchase #5	$100.67	11.412%	$112.1585	$112.16	$112.15	$112.20
Purchase #6	$127.39	8.682%	$138.45	$138.45	$138.45	$138.50
Purchase #7	$55.79	12.215%	$62.6047	$62.60	$62.60	$62.60
7 purchase totals =	$751.26		$812.4546	$812.46	$812.45	$812.50