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	$249.67	3.583%	$258.6157	$258.62	$258.60	$258.60
Purchase #2	$36.98	9.801%	$40.6044	$40.60	$40.60	$40.60
Purchase #3	$162.43	8.627%	$176.4428	$176.44	$176.45	$176.40
Purchase #4	$73.48	12.188%	$82.4357	$82.44	$82.45	$82.40
Purchase #5	$49.71	9.456%	$54.4106	$54.41	$54.40	$54.40
Purchase #6	$60.85	4.734%	$63.7306	$63.73	$63.75	$63.70
Purchase #7	$153.75	4.437%	$160.5719	$160.57	$160.55	$160.60
7 purchase totals =	$786.87		$836.8117	$836.81	$836.80	$836.70