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	$240.57	5.695%	$254.2705	$254.27	$254.25	$254.30
Purchase #2	$68.41	6.542%	$72.8854	$72.89	$72.90	$72.90
Purchase #3	$106.89	10.592%	$118.2118	$118.21	$118.20	$118.20
Purchase #4	$44.75	9.462%	$48.9842	$48.98	$49.00	$49.00
Purchase #5	$136.57	4.321%	$142.4712	$142.47	$142.45	$142.50
Purchase #6	$246.56	13.354%	$279.4856	$279.49	$279.50	$279.50
Purchase #7	$74.97	7.534%	$80.6182	$80.62	$80.60	$80.60
7 purchase totals =	$918.72		$996.9269	$996.93	$996.90	$997.00