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	$136.74	7.334%	$146.7685	$146.77	$146.75	$146.80
Purchase #2	$164.79	12.862%	$185.9853	$185.99	$186.00	$186.00
Purchase #3	$36.91	10.368%	$40.7368	$40.74	$40.75	$40.70
Purchase #4	$86.88	4.486%	$90.7774	$90.78	$90.80	$90.80
Purchase #5	$29.78	5.632%	$31.4572	$31.46	$31.45	$31.50
Purchase #6	$66.83	10.143%	$73.6086	$73.61	$73.60	$73.60
Purchase #7	$90.47	10.603%	$100.0625	$100.06	$100.05	$100.10
7 purchase totals =	$612.40		$669.3963	$669.41	$669.40	$669.50