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	$90.53	9.226%	$98.8823	$98.88	$98.90	$98.90
Purchase #2	$230.46	11.318%	$256.5435	$256.54	$256.55	$256.50
Purchase #3	$188.64	11.553%	$210.4336	$210.43	$210.45	$210.40
Purchase #4	$249.68	12.230%	$280.2159	$280.22	$280.20	$280.20
Purchase #5	$39.27	6.327%	$41.7546	$41.75	$41.75	$41.80
Purchase #6	$195.67	13.654%	$222.3868	$222.39	$222.40	$222.40
Purchase #7	$23.50	10.195%	$25.8958	$25.90	$25.90	$25.90
7 purchase totals =	$1,017.75		$1,136.1125	$1,136.11	$1,136.15	$1,136.10