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	$47.59	11.838%	$53.2237	$53.22	$53.20	$53.20
Purchase #2	$201.38	5.464%	$212.3834	$212.38	$212.40	$212.40
Purchase #3	$71.61	8.687%	$77.8308	$77.83	$77.85	$77.80
Purchase #4	$94.64	4.774%	$99.1581	$99.16	$99.15	$99.20
Purchase #5	$24.86	9.109%	$27.1245	$27.12	$27.10	$27.10
Purchase #6	$165.48	10.268%	$182.4715	$182.47	$182.45	$182.50
Purchase #7	$82.88	9.402%	$90.6724	$90.67	$90.65	$90.70
7 purchase totals =	$688.44		$742.8644	$742.85	$742.80	$742.90