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	$66.29	10.870%	$73.4957	$73.50	$73.50	$73.50
Purchase #2	$21.48	9.715%	$23.5668	$23.57	$23.55	$23.60
Purchase #3	$203.90	3.330%	$210.6899	$210.69	$210.70	$210.70
Purchase #4	$99.32	12.839%	$112.0717	$112.07	$112.05	$112.10
Purchase #5	$77.35	6.646%	$82.4907	$82.49	$82.50	$82.50
Purchase #6	$5.92	12.192%	$6.6418	$6.64	$6.65	$6.60
Purchase #7	$48.35	4.131%	$50.3473	$50.35	$50.35	$50.30
7 purchase totals =	$522.61		$559.3039	$559.31	$559.30	$559.30