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	$171.94	8.495%	$186.5463	$186.55	$186.55	$186.50
Purchase #2	$199.66	13.490%	$226.5941	$226.59	$226.60	$226.60
Purchase #3	$178.83	11.490%	$199.3776	$199.38	$199.40	$199.40
Purchase #4	$128.78	4.242%	$134.2428	$134.24	$134.25	$134.20
Purchase #5	$48.90	13.562%	$55.5318	$55.53	$55.55	$55.50
Purchase #6	$173.34	6.736%	$185.0162	$185.02	$185.00	$185.00
Purchase #7	$126.91	3.579%	$131.4521	$131.45	$131.45	$131.50
7 purchase totals =	$1,028.36		$1,118.7609	$1,118.76	$1,118.80	$1,118.70