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	$120.50	5.725%	$127.3986	$127.40	$127.40	$127.40
Purchase #2	$126.27	7.364%	$135.5685	$135.57	$135.55	$135.60
Purchase #3	$67.46	7.786%	$72.7124	$72.71	$72.70	$72.70
Purchase #4	$21.51	12.396%	$24.1764	$24.18	$24.20	$24.20
Purchase #5	$100.69	4.846%	$105.5694	$105.57	$105.55	$105.60
Purchase #6	$58.40	7.278%	$62.6504	$62.65	$62.65	$62.70
Purchase #7	$240.31	8.508%	$260.7556	$260.76	$260.75	$260.80
7 purchase totals =	$735.14		$788.8313	$788.84	$788.80	$789.00