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	$111.63	10.451%	$123.2965	$123.30	$123.30	$123.30
Purchase #2	$116.95	5.273%	$123.1168	$123.12	$123.10	$123.10
Purchase #3	$225.49	6.590%	$240.3498	$240.35	$240.35	$240.30
Purchase #4	$35.66	6.756%	$38.0692	$38.07	$38.05	$38.10
Purchase #5	$160.90	7.217%	$172.5122	$172.51	$172.50	$172.50
Purchase #6	$137.79	13.798%	$156.8023	$156.80	$156.80	$156.80
Purchase #7	$72.88	4.187%	$75.9315	$75.93	$75.95	$75.90
7 purchase totals =	$861.30		$930.0783	$930.08	$930.05	$930.00