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	$232.83	9.844%	$255.7498	$255.75	$255.75	$255.70
Purchase #2	$30.26	4.164%	$31.52	$31.52	$31.50	$31.50
Purchase #3	$161.90	11.577%	$180.6432	$180.64	$180.65	$180.60
Purchase #4	$216.79	3.125%	$223.5647	$223.56	$223.55	$223.60
Purchase #5	$100.59	4.757%	$105.3751	$105.38	$105.40	$105.40
Purchase #6	$90.27	9.240%	$98.6109	$98.61	$98.60	$98.60
Purchase #7	$65.98	4.575%	$68.9986	$69.00	$69.00	$69.00
7 purchase totals =	$898.62		$964.4623	$964.46	$964.45	$964.40