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	$230.48	5.146%	$242.3405	$242.34	$242.35	$242.30
Purchase #2	$66.92	6.782%	$71.4585	$71.46	$71.45	$71.50
Purchase #3	$134.67	10.530%	$148.8508	$148.85	$148.85	$148.90
Purchase #4	$205.27	7.383%	$220.4251	$220.43	$220.45	$220.40
Purchase #5	$41.63	3.357%	$43.0275	$43.03	$43.05	$43.00
Purchase #6	$89.69	12.166%	$100.6017	$100.60	$100.60	$100.60
Purchase #7	$157.44	4.604%	$164.6885	$164.69	$164.70	$164.70
7 purchase totals =	$926.10		$991.3926	$991.40	$991.45	$991.40