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	$116.86	9.790%	$128.3006	$128.30	$128.30	$128.30
Purchase #2	$246.55	13.102%	$278.853	$278.85	$278.85	$278.90
Purchase #3	$69.37	5.113%	$72.9169	$72.92	$72.90	$72.90
Purchase #4	$180.38	4.369%	$188.2608	$188.26	$188.25	$188.30
Purchase #5	$97.42	5.275%	$102.5589	$102.56	$102.55	$102.60
Purchase #6	$185.53	3.433%	$191.8992	$191.90	$191.90	$191.90
Purchase #7	$221.58	13.653%	$251.8323	$251.83	$251.85	$251.80
7 purchase totals =	$1,117.69		$1,214.6217	$1,214.62	$1,214.60	$1,214.70