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	$83.26	9.453%	$91.1306	$91.13	$91.15	$91.10
Purchase #2	$109.55	12.700%	$123.4629	$123.46	$123.45	$123.50
Purchase #3	$37.68	12.760%	$42.488	$42.49	$42.50	$42.50
Purchase #4	$230.84	12.773%	$260.3252	$260.33	$260.35	$260.30
Purchase #5	$162.92	5.342%	$171.6232	$171.62	$171.60	$171.60
Purchase #6	$132.47	7.806%	$142.8106	$142.81	$142.80	$142.80
Purchase #7	$18.97	5.406%	$19.9955	$20.00	$20.00	$20.00
7 purchase totals =	$775.69		$851.8360	$851.84	$851.85	$851.80