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	$126.94	7.632%	$136.6281	$136.63	$136.65	$136.60
Purchase #2	$46.59	3.713%	$48.3199	$48.32	$48.30	$48.30
Purchase #3	$208.34	9.158%	$227.4198	$227.42	$227.40	$227.40
Purchase #4	$7.31	10.322%	$8.0645	$8.06	$8.05	$8.10
Purchase #5	$77.90	4.192%	$81.1656	$81.17	$81.15	$81.20
Purchase #6	$158.89	4.807%	$166.5278	$166.53	$166.55	$166.50
Purchase #7	$115.85	13.524%	$131.5176	$131.52	$131.50	$131.50
7 purchase totals =	$741.82		$799.6433	$799.65	$799.60	$799.60