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	$162.92	10.729%	$180.3997	$180.40	$180.40	$180.40
Purchase #2	$193.98	3.512%	$200.7926	$200.79	$200.80	$200.80
Purchase #3	$226.70	4.828%	$237.6451	$237.65	$237.65	$237.60
Purchase #4	$164.43	4.223%	$171.3739	$171.37	$171.35	$171.40
Purchase #5	$157.56	10.599%	$174.2598	$174.26	$174.25	$174.30
Purchase #6	$238.97	13.149%	$270.3922	$270.39	$270.40	$270.40
Purchase #7	$61.56	6.839%	$65.7701	$65.77	$65.75	$65.80
7 purchase totals =	$1,206.12		$1,300.6334	$1,300.63	$1,300.60	$1,300.70