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	$44.93	13.199%	$50.8603	$50.86	$50.85	$50.90
Purchase #2	$83.27	8.584%	$90.4179	$90.42	$90.40	$90.40
Purchase #3	$56.26	6.592%	$59.9687	$59.97	$59.95	$60.00
Purchase #4	$87.88	3.426%	$90.8908	$90.89	$90.90	$90.90
Purchase #5	$134.76	6.238%	$143.1663	$143.17	$143.15	$143.20
Purchase #6	$7.96	5.526%	$8.3999	$8.40	$8.40	$8.40
Purchase #7	$38.62	5.558%	$40.7665	$40.77	$40.75	$40.80
7 purchase totals =	$453.68		$484.4704	$484.48	$484.40	$484.60