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	$99.58	7.371%	$106.92	$106.92	$106.90	$106.90
Purchase #2	$137.87	13.477%	$156.4507	$156.45	$156.45	$156.50
Purchase #3	$46.40	9.427%	$50.7741	$50.77	$50.75	$50.80
Purchase #4	$113.71	7.816%	$122.5976	$122.60	$122.60	$122.60
Purchase #5	$138.92	3.285%	$143.4835	$143.48	$143.50	$143.50
Purchase #6	$118.75	4.333%	$123.8954	$123.90	$123.90	$123.90
Purchase #7	$115.27	3.271%	$119.0405	$119.04	$119.05	$119.00
7 purchase totals =	$770.50		$823.1618	$823.16	$823.15	$823.20