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	$126.45	13.726%	$143.8065	$143.81	$143.80	$143.80
Purchase #2	$144.72	13.580%	$164.373	$164.37	$164.35	$164.40
Purchase #3	$40.70	4.527%	$42.5425	$42.54	$42.55	$42.50
Purchase #4	$156.43	11.271%	$174.0612	$174.06	$174.05	$174.10
Purchase #5	$44.48	13.446%	$50.4608	$50.46	$50.45	$50.50
Purchase #6	$31.26	3.416%	$32.3278	$32.33	$32.35	$32.30
Purchase #7	$192.79	6.243%	$204.8259	$204.83	$204.85	$204.80
7 purchase totals =	$736.83		$812.3977	$812.40	$812.40	$812.40