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	$29.44	10.796%	$32.6183	$32.62	$32.60	$32.60
Purchase #2	$160.37	9.651%	$175.8473	$175.85	$175.85	$175.80
Purchase #3	$123.68	7.372%	$132.7977	$132.80	$132.80	$132.80
Purchase #4	$142.56	12.501%	$160.3814	$160.38	$160.40	$160.40
Purchase #5	$59.54	9.685%	$65.3064	$65.31	$65.30	$65.30
Purchase #6	$132.47	13.242%	$150.0117	$150.01	$150.00	$150.00
Purchase #7	$100.45	11.645%	$112.1474	$112.15	$112.15	$112.10
7 purchase totals =	$748.51		$829.1102	$829.12	$829.10	$829.00