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	$239.47	11.241%	$266.3888	$266.39	$266.40	$266.40
Purchase #2	$72.78	7.303%	$78.0951	$78.10	$78.10	$78.10
Purchase #3	$225.28	12.652%	$253.7824	$253.78	$253.80	$253.80
Purchase #4	$10.34	12.759%	$11.6593	$11.66	$11.65	$11.70
Purchase #5	$173.98	8.214%	$188.2707	$188.27	$188.25	$188.30
Purchase #6	$9.61	9.818%	$10.5535	$10.55	$10.55	$10.60
Purchase #7	$178.34	9.354%	$195.0219	$195.02	$195.00	$195.00
7 purchase totals =	$909.80		$1,003.7717	$1,003.77	$1,003.75	$1,003.90