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	$123.72	3.456%	$127.9958	$128.00	$128.00	$128.00
Purchase #2	$42.37	8.701%	$46.0566	$46.06	$46.05	$46.10
Purchase #3	$68.55	12.522%	$77.1338	$77.13	$77.15	$77.10
Purchase #4	$54.92	13.800%	$62.499	$62.50	$62.50	$62.50
Purchase #5	$225.57	11.676%	$251.9076	$251.91	$251.90	$251.90
Purchase #6	$246.38	6.788%	$263.1043	$263.10	$263.10	$263.10
Purchase #7	$92.63	8.159%	$100.1877	$100.19	$100.20	$100.20
7 purchase totals =	$854.14		$928.8848	$928.89	$928.90	$928.90