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	$7.27	9.715%	$7.9763	$7.98	$8.00	$8.00
Purchase #2	$59.90	11.170%	$66.5908	$66.59	$66.60	$66.60
Purchase #3	$51.45	10.864%	$57.0395	$57.04	$57.05	$57.00
Purchase #4	$52.77	13.432%	$59.8581	$59.86	$59.85	$59.90
Purchase #5	$112.95	10.262%	$124.5409	$124.54	$124.55	$124.50
Purchase #6	$99.86	7.187%	$107.0369	$107.04	$107.05	$107.00
Purchase #7	$169.84	12.581%	$191.2076	$191.21	$191.20	$191.20
7 purchase totals =	$554.04		$614.2501	$614.26	$614.30	$614.20