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	$76.51	10.330%	$84.4135	$84.41	$84.40	$84.40
Purchase #2	$100.90	5.183%	$106.1296	$106.13	$106.15	$106.10
Purchase #3	$43.38	4.645%	$45.395	$45.40	$45.40	$45.40
Purchase #4	$236.73	5.864%	$250.6118	$250.61	$250.60	$250.60
Purchase #5	$103.27	12.497%	$116.1757	$116.18	$116.20	$116.20
Purchase #6	$99.52	4.246%	$103.7456	$103.75	$103.75	$103.70
Purchase #7	$83.83	13.649%	$95.272	$95.27	$95.25	$95.30
7 purchase totals =	$744.14		$801.7432	$801.75	$801.75	$801.70