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	$26.26	11.308%	$29.2295	$29.23	$29.25	$29.20
Purchase #2	$113.25	12.662%	$127.5897	$127.59	$127.60	$127.60
Purchase #3	$48.79	3.825%	$50.6562	$50.66	$50.65	$50.70
Purchase #4	$183.62	7.111%	$196.6772	$196.68	$196.70	$196.70
Purchase #5	$204.46	11.366%	$227.6989	$227.70	$227.70	$227.70
Purchase #6	$156.52	8.308%	$169.5237	$169.52	$169.50	$169.50
Purchase #7	$91.48	12.157%	$102.6012	$102.60	$102.60	$102.60
7 purchase totals =	$824.38		$903.9764	$903.98	$904.00	$904.00