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	$97.43	11.166%	$108.309	$108.31	$108.30	$108.30
Purchase #2	$243.94	5.283%	$256.8274	$256.83	$256.85	$256.80
Purchase #3	$125.83	4.786%	$131.8522	$131.85	$131.85	$131.90
Purchase #4	$174.80	13.589%	$198.5536	$198.55	$198.55	$198.60
Purchase #5	$62.45	7.428%	$67.0888	$67.09	$67.10	$67.10
Purchase #6	$194.28	12.742%	$219.0352	$219.04	$219.05	$219.00
Purchase #7	$42.75	6.806%	$45.6596	$45.66	$45.65	$45.70
7 purchase totals =	$941.48		$1,027.3258	$1,027.33	$1,027.35	$1,027.40