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	$19.93	8.646%	$21.6531	$21.65	$21.65	$21.70
Purchase #2	$57.64	6.511%	$61.3929	$61.39	$61.40	$61.40
Purchase #3	$183.27	3.717%	$190.0821	$190.08	$190.10	$190.10
Purchase #4	$185.73	5.849%	$196.5933	$196.59	$196.60	$196.60
Purchase #5	$193.51	11.611%	$215.9784	$215.98	$216.00	$216.00
Purchase #6	$237.62	6.869%	$253.9421	$253.94	$253.95	$253.90
Purchase #7	$78.57	12.675%	$88.5287	$88.53	$88.55	$88.50
7 purchase totals =	$956.27		$1,028.1706	$1,028.16	$1,028.25	$1,028.20