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	$178.49	5.644%	$188.564	$188.56	$188.55	$188.60
Purchase #2	$174.96	13.342%	$198.3032	$198.30	$198.30	$198.30
Purchase #3	$75.76	7.431%	$81.3897	$81.39	$81.40	$81.40
Purchase #4	$115.85	13.814%	$131.8535	$131.85	$131.85	$131.90
Purchase #5	$43.46	4.609%	$45.4631	$45.46	$45.45	$45.50
Purchase #6	$100.82	6.615%	$107.4892	$107.49	$107.50	$107.50
Purchase #7	$41.68	5.135%	$43.8203	$43.82	$43.80	$43.80
7 purchase totals =	$731.02		$796.8830	$796.87	$796.85	$797.00