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	$14.78	3.374%	$15.2787	$15.28	$15.30	$15.30
Purchase #2	$145.86	13.593%	$165.6867	$165.69	$165.70	$165.70
Purchase #3	$239.45	4.368%	$249.9092	$249.91	$249.90	$249.90
Purchase #4	$151.60	5.855%	$160.4762	$160.48	$160.50	$160.50
Purchase #5	$62.34	8.453%	$67.6096	$67.61	$67.60	$67.60
Purchase #6	$218.98	13.529%	$248.6058	$248.61	$248.60	$248.60
Purchase #7	$236.61	12.178%	$265.4244	$265.42	$265.40	$265.40
7 purchase totals =	$1,069.62		$1,172.9906	$1,173.00	$1,173.00	$1,173.00