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	$21.68	7.623%	$23.3327	$23.33	$23.35	$23.30
Purchase #2	$137.27	9.857%	$150.8007	$150.80	$150.80	$150.80
Purchase #3	$148.34	3.724%	$153.8642	$153.86	$153.85	$153.90
Purchase #4	$123.89	5.745%	$131.0075	$131.01	$131.00	$131.00
Purchase #5	$179.83	5.677%	$190.0389	$190.04	$190.05	$190.00
Purchase #6	$15.44	12.290%	$17.3376	$17.34	$17.35	$17.30
Purchase #7	$99.73	4.458%	$104.176	$104.18	$104.20	$104.20
7 purchase totals =	$726.18		$770.5576	$770.56	$770.60	$770.50