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	$229.86	3.682%	$238.3234	$238.32	$238.30	$238.30
Purchase #2	$235.95	5.705%	$249.4109	$249.41	$249.40	$249.40
Purchase #3	$85.68	5.239%	$90.1688	$90.17	$90.15	$90.20
Purchase #4	$12.27	10.570%	$13.5669	$13.57	$13.55	$13.60
Purchase #5	$96.98	13.471%	$110.0442	$110.04	$110.05	$110.00
Purchase #6	$223.85	3.449%	$231.5706	$231.57	$231.55	$231.60
Purchase #7	$116.85	12.798%	$131.8045	$131.80	$131.80	$131.80
7 purchase totals =	$1,001.44		$1,064.8893	$1,064.88	$1,064.80	$1,064.90