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	$199.47	9.308%	$218.0367	$218.04	$218.05	$218.00
Purchase #2	$66.79	8.805%	$72.6709	$72.67	$72.65	$72.70
Purchase #3	$231.41	4.709%	$242.3071	$242.31	$242.30	$242.30
Purchase #4	$40.39	12.202%	$45.3184	$45.32	$45.30	$45.30
Purchase #5	$110.27	6.547%	$117.4894	$117.49	$117.50	$117.50
Purchase #6	$55.56	12.159%	$62.3155	$62.32	$62.30	$62.30
Purchase #7	$116.26	4.793%	$121.8323	$121.83	$121.85	$121.80
7 purchase totals =	$820.15		$879.9703	$879.98	$879.95	$879.90