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	$105.40	10.437%	$116.4006	$116.40	$116.40	$116.40
Purchase #2	$36.78	9.265%	$40.1877	$40.19	$40.20	$40.20
Purchase #3	$235.31	12.362%	$264.399	$264.40	$264.40	$264.40
Purchase #4	$130.61	9.772%	$143.3732	$143.37	$143.35	$143.40
Purchase #5	$62.57	4.175%	$65.1823	$65.18	$65.20	$65.20
Purchase #6	$197.37	10.577%	$218.2458	$218.25	$218.25	$218.20
Purchase #7	$60.72	8.726%	$66.0184	$66.02	$66.00	$66.00
7 purchase totals =	$828.76		$913.8070	$913.81	$913.80	$913.80