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	$70.90	11.413%	$78.9918	$78.99	$79.00	$79.00
Purchase #2	$199.60	9.339%	$218.2406	$218.24	$218.25	$218.20
Purchase #3	$59.79	11.398%	$66.6049	$66.60	$66.60	$66.60
Purchase #4	$84.43	4.693%	$88.3923	$88.39	$88.40	$88.40
Purchase #5	$20.86	10.570%	$23.0649	$23.06	$23.05	$23.10
Purchase #6	$73.96	6.567%	$78.817	$78.82	$78.80	$78.80
Purchase #7	$104.81	11.576%	$116.9428	$116.94	$116.95	$116.90
7 purchase totals =	$614.35		$671.0543	$671.04	$671.05	$671.00