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	$41.72	12.142%	$46.7856	$46.79	$46.80	$46.80
Purchase #2	$182.26	8.566%	$197.8724	$197.87	$197.85	$197.90
Purchase #3	$81.85	10.567%	$90.4991	$90.50	$90.50	$90.50
Purchase #4	$128.35	8.451%	$139.1969	$139.20	$139.20	$139.20
Purchase #5	$93.82	6.735%	$100.1388	$100.14	$100.15	$100.10
Purchase #6	$212.77	12.211%	$238.7513	$238.75	$238.75	$238.80
Purchase #7	$39.92	6.523%	$42.524	$42.52	$42.50	$42.50
7 purchase totals =	$780.69		$855.7681	$855.77	$855.75	$855.80