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	$188.34	5.641%	$198.9643	$198.96	$198.95	$199.00
Purchase #2	$19.50	5.791%	$20.6292	$20.63	$20.65	$20.60
Purchase #3	$151.68	12.861%	$171.1876	$171.19	$171.20	$171.20
Purchase #4	$107.50	10.243%	$118.5112	$118.51	$118.50	$118.50
Purchase #5	$170.93	12.236%	$191.845	$191.85	$191.85	$191.80
Purchase #6	$17.70	9.774%	$19.43	$19.43	$19.45	$19.40
Purchase #7	$115.96	6.869%	$123.9253	$123.93	$123.95	$123.90
7 purchase totals =	$771.61		$844.4926	$844.50	$844.55	$844.40