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	$228.32	12.107%	$255.9627	$255.96	$255.95	$256.00
Purchase #2	$221.83	5.196%	$233.3563	$233.36	$233.35	$233.40
Purchase #3	$122.42	4.286%	$127.6669	$127.67	$127.65	$127.70
Purchase #4	$127.45	6.612%	$135.877	$135.88	$135.90	$135.90
Purchase #5	$83.77	8.659%	$91.0236	$91.02	$91.00	$91.00
Purchase #6	$142.87	12.625%	$160.9073	$160.91	$160.90	$160.90
Purchase #7	$24.69	3.813%	$25.6314	$25.63	$25.65	$25.60
7 purchase totals =	$951.35		$1,030.4252	$1,030.43	$1,030.40	$1,030.50