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	$120.48	10.515%	$133.1485	$133.15	$133.15	$133.10
Purchase #2	$41.90	4.304%	$43.7034	$43.70	$43.70	$43.70
Purchase #3	$158.76	13.155%	$179.6449	$179.64	$179.65	$179.60
Purchase #4	$131.41	11.487%	$146.5051	$146.51	$146.50	$146.50
Purchase #5	$239.38	7.872%	$258.224	$258.22	$258.20	$258.20
Purchase #6	$40.32	6.759%	$43.0452	$43.05	$43.05	$43.00
Purchase #7	$134.98	13.242%	$152.8541	$152.85	$152.85	$152.90
7 purchase totals =	$867.23		$957.1252	$957.12	$957.10	$957.00