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	$241.79	4.753%	$253.2823	$253.28	$253.30	$253.30
Purchase #2	$178.41	11.418%	$198.7809	$198.78	$198.80	$198.80
Purchase #3	$122.90	7.175%	$131.7181	$131.72	$131.70	$131.70
Purchase #4	$216.67	10.118%	$238.5927	$238.59	$238.60	$238.60
Purchase #5	$45.75	8.537%	$49.6557	$49.66	$49.65	$49.70
Purchase #6	$81.31	10.109%	$89.5296	$89.53	$89.55	$89.50
Purchase #7	$13.55	12.611%	$15.2588	$15.26	$15.25	$15.30
7 purchase totals =	$900.38		$976.8181	$976.82	$976.85	$976.90