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	$239.27	13.699%	$272.0476	$272.05	$272.05	$272.00
Purchase #2	$55.81	9.813%	$61.2866	$61.29	$61.30	$61.30
Purchase #3	$48.99	3.211%	$50.5631	$50.56	$50.55	$50.60
Purchase #4	$130.38	12.149%	$146.2199	$146.22	$146.20	$146.20
Purchase #5	$169.81	9.694%	$186.2714	$186.27	$186.25	$186.30
Purchase #6	$189.56	4.817%	$198.6911	$198.69	$198.70	$198.70
Purchase #7	$218.46	4.150%	$227.5261	$227.53	$227.55	$227.50
7 purchase totals =	$1,052.28		$1,142.6058	$1,142.61	$1,142.60	$1,142.60