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	$47.49	6.441%	$50.5488	$50.55	$50.55	$50.50
Purchase #2	$229.52	11.416%	$255.722	$255.72	$255.70	$255.70
Purchase #3	$165.68	13.399%	$187.8795	$187.88	$187.90	$187.90
Purchase #4	$51.66	11.541%	$57.6221	$57.62	$57.60	$57.60
Purchase #5	$87.94	10.828%	$97.4621	$97.46	$97.45	$97.50
Purchase #6	$181.89	10.260%	$200.5519	$200.55	$200.55	$200.60
Purchase #7	$154.45	8.376%	$167.3867	$167.39	$167.40	$167.40
7 purchase totals =	$918.63		$1,017.1731	$1,017.17	$1,017.15	$1,017.20