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	$139.69	12.246%	$156.7964	$156.80	$156.80	$156.80
Purchase #2	$135.37	12.338%	$152.072	$152.07	$152.05	$152.10
Purchase #3	$146.86	12.591%	$165.3511	$165.35	$165.35	$165.40
Purchase #4	$193.46	11.304%	$215.3287	$215.33	$215.35	$215.30
Purchase #5	$98.82	9.193%	$107.9045	$107.90	$107.90	$107.90
Purchase #6	$129.61	7.146%	$138.8719	$138.87	$138.85	$138.90
Purchase #7	$131.39	6.136%	$139.4521	$139.45	$139.45	$139.50
7 purchase totals =	$975.20		$1,075.7767	$1,075.77	$1,075.75	$1,075.90