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	$78.49	7.797%	$84.6099	$84.61	$84.60	$84.60
Purchase #2	$242.46	9.330%	$265.0815	$265.08	$265.10	$265.10
Purchase #3	$99.34	13.383%	$112.6347	$112.63	$112.65	$112.60
Purchase #4	$46.62	13.830%	$53.0675	$53.07	$53.05	$53.10
Purchase #5	$82.79	8.508%	$89.8338	$89.83	$89.85	$89.80
Purchase #6	$127.85	10.340%	$141.0697	$141.07	$141.05	$141.10
Purchase #7	$134.54	13.506%	$152.711	$152.71	$152.70	$152.70
7 purchase totals =	$812.09		$899.0081	$899.00	$899.00	$899.00