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	$249.92	12.667%	$281.5774	$281.58	$281.60	$281.60
Purchase #2	$70.85	3.485%	$73.3191	$73.32	$73.30	$73.30
Purchase #3	$127.89	12.678%	$144.1039	$144.10	$144.10	$144.10
Purchase #4	$91.26	9.601%	$100.0219	$100.02	$100.00	$100.00
Purchase #5	$165.48	6.216%	$175.7662	$175.77	$175.75	$175.80
Purchase #6	$239.98	9.726%	$263.3205	$263.32	$263.30	$263.30
Purchase #7	$13.58	5.219%	$14.2887	$14.29	$14.30	$14.30
7 purchase totals =	$958.96		$1,052.3977	$1,052.40	$1,052.35	$1,052.40