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	$80.67	6.329%	$85.7756	$85.78	$85.80	$85.80
Purchase #2	$47.41	12.712%	$53.4368	$53.44	$53.45	$53.40
Purchase #3	$119.45	4.321%	$124.6114	$124.61	$124.60	$124.60
Purchase #4	$169.69	7.720%	$182.7901	$182.79	$182.80	$182.80
Purchase #5	$107.74	9.644%	$118.1304	$118.13	$118.15	$118.10
Purchase #6	$215.48	10.136%	$237.3211	$237.32	$237.30	$237.30
Purchase #7	$92.87	7.143%	$99.5037	$99.50	$99.50	$99.50
7 purchase totals =	$833.31		$901.5691	$901.57	$901.60	$901.50