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	$74.49	9.399%	$81.4913	$81.49	$81.50	$81.50
Purchase #2	$85.46	4.289%	$89.1254	$89.13	$89.15	$89.10
Purchase #3	$65.47	9.360%	$71.598	$71.60	$71.60	$71.60
Purchase #4	$29.84	10.726%	$33.0406	$33.04	$33.05	$33.00
Purchase #5	$38.57	5.585%	$40.7241	$40.72	$40.70	$40.70
Purchase #6	$220.98	3.803%	$229.3839	$229.38	$229.40	$229.40
Purchase #7	$36.60	10.309%	$40.3731	$40.37	$40.35	$40.40
7 purchase totals =	$551.41		$585.7364	$585.73	$585.75	$585.70