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	$43.33	3.859%	$45.0021	$45.00	$45.00	$45.00
Purchase #2	$31.92	5.770%	$33.7618	$33.76	$33.75	$33.80
Purchase #3	$74.94	10.343%	$82.691	$82.69	$82.70	$82.70
Purchase #4	$148.49	8.488%	$161.0938	$161.09	$161.10	$161.10
Purchase #5	$121.30	6.661%	$129.3798	$129.38	$129.40	$129.40
Purchase #6	$68.28	6.622%	$72.8015	$72.80	$72.80	$72.80
Purchase #7	$30.69	3.691%	$31.8228	$31.82	$31.80	$31.80
7 purchase totals =	$518.95		$556.5528	$556.54	$556.55	$556.60